You can of course do this many different ways. Some questions can be asked to help find the best solution for you. When do you want the content to load? How often will the content change?
I would generally recommend this be part of an MVC app. In the controller you could listen for an event such as activate on the panel then run the ajax request. In the callback you can use the panel's setHtml method to set the data. Alternately if you specify a template on the panel, you'd use the setData method.
If this doesn't get you on your way, post more details about your app and what you want to accomplish.