Warm a fry pan that will hold the two slices of bread. Keep at an even medium heat
Slice each slice through its thickness but not all the way. Leave on edge as a hinge. Insert half the cheese and onion in each pocket.
Mix eggs and milk, salt and pepper in a wide dish. Soak the stuffed slices in the mixture for a couple of minutes on both sides until all the mixture is absorbed.
Meanwhile, sauté the slices of apple in olive oil in pan over medium heat until slightly golden.
Place the soaked slices on the apple and fry until browned. Flip.
Cook on second side until browned, and the cheese inside is melted.
Can be served with a fried egg for traditional breakfast fare, or with vegetable for more brunchy feel.
Two large servings.