How do you change the food on the menu?

To change the menu you need to have a hero assigned to the kitchen. To upgrade the food menu to a hearty meal that hero needs to be at least level 15. In the meantime until you can get that you can make sure you have enough hunters and your kitchen is well staffed so that you can produce enough basic meals for the amount of survivors your camp has. They will still not be full after meals but you should be able to get thru long enough to upgrade your hero and your kitchen.