Use a squished "O" hand as if stuffing a piece of food into your mouth.
(Keep your mouth closed though. Thanks.)
The sign for "eat" and the sign for "food" are used pretty much interchangeably. Technically the sign
eat should be a single motion, and the sign for food should be a double motion
(if you consider these signs a noun/verb pair). But what about the concept
of "eating?" I use a double motion to indicate a process is
taking place. How about "pig out?" For that I use both hands. In any case, I wouldn't get uptight about this sign.
If your teacher wants it one way or the other...do it his/her way. If you get
corrected by a Deaf person, just smile and try to remember to sign it that
way around that person.
Sentence: "What is your favorite food?"
= YOUR FAVORITE FOOD WHAT?