Heat a large frying pan with vegetable oil, just enough to coat the bottom. Fry plantains for 2-3 minutes on each side or until golden and slightly crispy. Drain on a plate with paper towel, set aside.
To assemble pastelon: Take your prepared square pan, start with a layer of plantains, then beef, then a fistful of cheese, repeat. You want to finish with cheese and plantains. Beat 3 eggs with 2 Tbs of milk, pour over the pastelón. Let it sit for a minute allowing the egg to soak in. Top off with just a bit more cheese.