You'll see the cooking bubble on the other side to the Baking bubble when you click on the oven.
It seems like most things are locked out to you and you can only cook one thing, but basically you have to use the same Sim to cook that one available thing over and over a few times, and this will unlock more options to cook.
Keep cooking to unlock more Items. Each time to cook something you will be rewarded with an item much like the backing Hobby.
Where do I find the Chopping Board? I have looked everywhere :(