Very easy. Step one: find and kill rabbits until you get meat. Step two: make a furnace out of 8 stone. Step three: cook the meat in the furnace using coal or wood products as fuel. Step four: eat the meat. (if you can't eat the meat then your food bar is full and you need to run around to make it drop. The food bar will NOT drop on peaceful so increase the difficulty to easy or harder to eat)
Edit: Comments are telling me it does not need to be eaten and therefore can be completed on peaceful. Thanks for the comments guys!