"이 요리는 뭐예요?"
Translation:What is this dish?
someone correct me if i'm wrong, but as i understand, there's a subtle difference between the two. in the example sentence the topic is "dish", hence the 는 in 요리는. i believe in your suggested sentence the topic is "this", which in korean would go more like "이것은 뭐 (not sure if -ㄹ is needed there) 요리예요?"
As far as i know, this statement CAN mean what you've wrote.
This kind of sentence is seen in 대구 사투리.
Context : Imagine you're in a restaurant having lunch but as soon as you see the dishes (They don't look as you've expected them to be; they look weird), you might say "이게 뭐예요?", "이 요리 뭐예요?"