New Twiddle

mirage.config.js

export default function() {
  //window.server = this;
  
  this.get('/foo', { data: "first response" });
  
  this.namespace = '/namespace1';
  this.get('/bar', { data: "second response" });
};

routes.application.js

import Ember from 'ember';

export default Ember.Route.extend({
  
  model() {
    return Ember.RSVP.hash({
      foo: Ember.$.getJSON('/foo'),
      bar: Ember.$.getJSON('/namespace1/bar')
    });
  }
  
  
});

templates.application.hbs

<h1>Mirage boilerplate</h1>

<div class='pa4'>
  <p>{{model.foo.data}}</p>
  <p>{{model.bar.data}}</p>
</div>

twiddle.json

{
  "version": "0.15.0",
  "ENV": {
    "ember-cli-mirage": {
      "enabled": true
    }
  },
  "EmberENV": {
    "FEATURES": {
      "ds-finder-include": true
    }
  },
  "options": {
    "use_pods": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.2.2",
    "ember-template-compiler": "3.2.2",
    "ember-testing": "3.2.2"
  },
  "addons": {
    "ember-data": "3.2.0",
    "ember-cli-mirage": "0.2.5"
  }
}