inner.html

<div>hola</div>

inner.js

define(['widget', 'template!inner.html'], function (Widget, template) {

   return Widget.extend({
       'sig/initialize': function (signal, deferred) {
           this.html(template, deferred);
       }
   });
});

outer.html

<div data-weave="inner.js"></div>

outer.js

define(['widget', 'template!outer.html'], function (Widget, template) {

   return Widget.extend({
       'sig/initialize': function (signal, deferred) {
           var me = this;

           $.Deferred(function (dfd) {
               me.html(template, dfd);
           }).then(function () {
               //Call inner api here
           }).then(deferred.resolve, deferred.reject, deferred.progress);
       }
   });
});