each-in

controllers.application.js

import Ember from 'ember';
import { computed } from '@ember/object'

export default Ember.Controller.extend({
  people: {
    'Mr. Chris': ['foo', 'bar'],
    'Mr. Tim': ['fiz', 'baz']
  },
  people2: computed(function(){
  	const out = {}
 	 	out['Mr. Chris'] = ['foo']
  	out['Mr. Chris'].pushObject('bar')
 	  out['Mr. Tim'] = ['fiz']
  	out['Mr. Tim'].pushObject('baz')
  	return out
  })
});

templates.application.hbs

{{#each-in people as |name things|}}
	{{name}}
  {{#each things as |thing|}}
    <br />{{thing}}
  {{/each}}
  <hr />
{{/each-in}}

{{#each-in people2 as |name things|}}
	{{name}}
  {{#each things as |thing|}}
    <br />{{thing}}
  {{/each}}
  <hr />
{{/each-in}}

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.12.0",
    "ember-template-compiler": "3.12.0",
    "ember-testing": "3.12.0"
  },
  "addons": {
    "ember-data": "3.12.0"
  }
}