best GUI option for my simple needs?

I'm brand new to C++/objC. I need to build an app on OSX Lion with xcode that has a very simple GUI. I'd like a fullscreen black window (no menu bar, scrolling, or resizing - just a black screen). In this window I'd like to have minimalist clickable buttons that are single color rectangles with text inside, in a custom layout. That's it. I'd prefer no other pre-designed GUI artifacts of any kind on screen.

As far as CPU usage, I'd like to find the most lightweight way of accomplishing this. Cocoa, wxWidgets? Is there a better option out there? Thanks for your help.