You are looking for an easy way to retrieve data from your CakePHP backend into Sencha Touch?
Check out Bancha, it uses Senchas Ext.Direct spec to transmit data.
You can easily load complete model configurations and data, just by using Bancha.onModelReady('User', callback);
For general questions about Bancha visit the ExtJS Forum Post
PS: I know this is a cross-post, but I feel this should not only be mentioned in the ExtJS Forums since it also applies to Sencha Touch.