I tried with a knife but was unsuccesful

Big pair of scissors. I've used these before and they worked.

Fold it.

Chainsaw.
Oh no - that's moussaka.

Snap it with your hands. Use superstrength.

Or use the force.

Cut a track down the middle before snapping in two. If too solid, place on work surface with half sticking out and press down sharply to break.

Of course, by now you could easily have made your own 😎

Cook it first?

Speaking from experience you end up eating the whole thing.