Just a little more info in case you have some experience with other GUI frameworks.
If you're wanting to run the GUI on an LCD or some kind of HDMI monitor, then you have any flavor of GUI toolkit available that you would find in a typical Linux environment (GTK, QT, FLTK...).
You can communicate with Bela using shared memory or just use sockets, similar to what giuliomoro suggested.
The network socket method has an appeal because you can run the GUI from any kind of device, like a smartphone, tablet, separate Raspberry Pi & touch interface, etc. I don't know your goal.
Either way you can run the Beaglebone as a typical desktop or tablet computer and do all your interactions without needing any separate devices if you want.
The only part Bela plays is just to pass the audio in real time and process it. In the end all you need is a method to communicate to your audio application and receive status from it -- also look at the OSC examples.