GUI for ATMEL AVR

Hello, I’m just an electronic hobbyist (and physic teacher). I’d like to make a sort of chronometer for my Go-Kart. It’s working fine now (using WinAVR as C compiler for a microcontroller (uC) ATMEL AVR ATmega8535) but I use a character LCD display. I would like to use a graphical LCD now. But I also would like to have some widgets (like in GTK+) Unfortunately I don’t know if it is possible to do it without a minimal Linux on the uC (I’m also fond of open source softwares and Linux… of course) I guess that having a Linux kernel is too much for a little 8 bits uC like ATMEL AVR so maybe FreeRTOS can be a solution for me. About the GUI, There is no mouse or touchscreen so the GUI should be like the GUI of a phone or any embedded device that’s to say that there is only - up/down/left/right buttons - ok button - cancel button I hope you could help me for this. Regards