'providers' => [
    //...
    NilPortugues\Laravel5\JsonApi\Laravel5JsonApiServiceProvider::class,
],

<?php
Route::group(['namespace' => 'Api'], function() {
    Route::resource('employees', 'EmployeesController');    
    Route::get(
        'employees/{employee_id}/orders', [
        'as' => 'employees.orders',
        'uses' => 'EmployeesController@getOrdersByEmployee'
    ]);
});
//...

<?php namespace App\Model\Database;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Foundation\Validation\ValidatesRequests;

class Employees extends Model
{
    public $timestamps = false;
    protected $table = 'employees';    
    protected $primaryKey = 'id';
    protected $appends = ['full_name'];

    /**
     * @return \Illuminate\Database\Eloquent\Relations\HasOne
     */
    public function latestOrders()
    {
        return $this->hasMany(Orders::class, 'employee_id')->limit(10);
    }

    /**
     * @return string
     */
    public function getFullNameAttribute()
    {
        return $this->first_name.' '.$this->last_name;
    }
}

<?php namespace App\Model\Database;

use Illuminate\Database\Eloquent\Model;

class Orders extends Model
{   
    public $timestamps = false;
    protected $table = 'orders';
    protected $primaryKey = 'id';

    /**
     * @return \Illuminate\Database\Eloquent\Relations\HasOne
     */
    public function employee()
    {
        return $this->belongsTo(Employees::class, 'employee_id');
    }
}

<?php namespace App\Model\Api;

use App\Model\Database\Employees;
use NilPortugues\Api\Mappings\JsonApiMapping;

class EmployeesTransformer implements JsonApiMapping
{
    /**
     * Returns a string with the full class name, including namespace.
     *
     * @return string
     */
    public function getClass()
    {
        return Employees::class;
    }

    /**
     * Returns a string representing the resource name 
     * as it will be shown after the mapping.
     *
     * @return string
     */
    public function getAlias()
    {
        return 'employee';
    }

    /**
     * Returns an array of properties that will be renamed.
     * Key is current property from the class. 
     * Value is the property's alias name.
     *
     * @return array
     */
    public function getAliasedProperties()
    {
        return [
            'last_name' => 'surname',
            
        ];
    }

    /**
     * List of properties in the class that will be  ignored by the mapping.
     *
     * @return array
     */
    public function getHideProperties()
    {
        return [
            'attachments'
        ];
    }

    /**
     * Returns an array of properties that are used as an ID value.
     *
     * @return array
     */
    public function getIdProperties()
    {
        return ['id'];
    }

    /**
     * Returns a list of URLs. This urls must have placeholders 
     * to be replaced with the getIdProperties() values.
     *
     * @return array
     */
    public function getUrls()
    {
        return [
            'self' => ['name' => 'employees.show', 'as_id' => 'id'],
            'employees' => ['name' => 'employees.index'],
            'employee_orders' => ['name' => 'employees.orders', 'as_id' => 'id']
        ];
    }

    /**
     * Returns an array containing the relationship mappings as an array.
     * Key for each relationship defined must match a property of the mapped class.
     *
     * @return array
     */
    public function getRelationships()
    {
        return [];
    }
} 

<?php namespace App\Model\Api;

use App\Model\Database\Orders;
use NilPortugues\Api\Mappings\JsonApiMapping;

class OrdersTransformer implements JsonApiMapping
{
    /**
     * {@inheritDoc}
     */
    public function getClass()
    {
        return Orders::class;
    }
    /**
     * {@inheritDoc}
     */
    public function getAlias()
    {
        return 'order';
    }
    /**
     * {@inheritDoc}
     */
    public function getAliasedProperties()
    {
        return [];
    }
    /**
     * {@inheritDoc}
     */
    public function getHideProperties()
    {
        return [];
    }
    /**
     * {@inheritDoc}
     */
    public function getIdProperties()
    {
        return ['id'];
    }
    /**
     * {@inheritDoc}
     */
    public function getUrls()
    {
        return [
            'self'     => ['name' => 'orders.show', 'as_id' => 'id'],
            'employee' => ['name' => 'employees.show', 'as_id' => 'employee_id'],
        ];
    }
    /**
     * {@inheritDoc}
     */
    public function getRelationships()
    {
        return [];
    }
    
    /**
     * List the fields that are mandatory in a persitence action (POST/PUT). 
     * If empty array is returned, all fields are mandatory.
     */
    public function getRequiredProperties()
    {
        return [];
    }    
} 

<?php
use App\Model\Api\EmployeesTransformer;
use App\Model\Api\OrdersTransformer;

return [
    EmployeesTransformer::class,
    OrdersTransformer::class,
];

$app->register(\NilPortugues\Laravel5\JsonApi\Laravel5JsonApiServiceProvider::class);
$app->configure('jsonapi');

$app->withFacades();

<?php
$app->group(
    ['namespace' => 'Api'], function($app) {
        $app->get(
            'employees', [
            'as' => 'employees.index',
            'uses' =>'EmployeesController@index'
        ]);
        $app->post(
            'employees', [
            'as' => 'employees.store',
            'uses' =>'EmployeesController@store'
        ]);
        $app->get(
            'employees/{employee_id}', [
            'as' => 'employees.show', 
            'uses' =>'EmployeesController@show'
        ]);
        $app->put(
            'employees/{employee_id}', [
            'as' => 'employees.update', 
            'uses' =>'EmployeesController@update'
        ]);
        $app->patch(
            'employees/{employee_id}', [
            'as' => 'employees.patch',
            'uses' =>'EmployeesController@update'
        ]);
        $app->delete(
            'employees/{employee_id}', [
            'as' => 'employees.destroy',
            'uses' =>'EmployeesController@destroy'
        ]);
        
        $app->get(
            'employees/{employee_id}/orders', [
            'as' => 'employees.orders', 
            'uses' => 'EmployeesController@getOrdersByEmployee'
        ]);
    }
);
//...