New Twiddle

components.comic-publishers.js

import Ember from 'ember';

export default Ember.Component.extend({
  actions: {
    selectSuperhero(pub, hero) {
      this.attrs.selectSuperhero(hero, pub);
    }
  }
});

components.superhero-list-item.js

import Ember from 'ember';

export default Ember.Component.extend({
  tagName: 'li',
  click() {
    this.attrs.select(this.get('hero'));
  }
});

components.superhero-list.js

import Ember from 'ember';

export default Ember.Component.extend({
  tagName: 'ul'
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  publishers: [
    Em.Object.create({
      name: 'DC Comics',
      superheroes: [
        Em.Object.create({name: "Batman"}),
        Em.Object.create({name: "Superman"}),
        Em.Object.create({name: "Flash"})
      ]}),
    Em.Object.create({
      name: 'Marvel Comics',
      superheroes: [
        Em.Object.create({name: "Iron Man"}),
        Em.Object.create({name: "Thor"}),
        Em.Object.create({name: "Black Widow"})
      ]})
  ],
  actions: {
    selectSuperhero(hero, publisher) {
      alert('selected ' + hero.get('name') + ' of ' + publisher.get('name'));
    }
  }
});

templates.application.hbs

<h1>Superheroes</h1>

{{comic-publishers publishers=publishers selectSuperhero=(action 'selectSuperhero')}}

templates.components.comic-publishers.hbs

{{#each publishers as |pub|}}
  <h2>{{pub.name}}</h2>
  {{superhero-list superheroes=pub.superheroes selectSuperhero=(action 'selectSuperhero' pub)}}
{{/each}}

templates.components.superhero-list-item.hbs

{{hero.name}}

templates.components.superhero-list.hbs

{{#each superheroes as |hero|}}
  {{superhero-list-item hero=hero select=attrs.selectSuperhero}}
{{/each}}

twiddle.json

{
  "version": "0.9.3",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.6.0",
    "ember-data": "2.6.1",
    "ember-template-compiler": "2.6.0"
  }
}