Preheat the oven to 200°C or 392°F (bottom and top heating with air circulation).
Clean the chicken breast. Wash it to remove any remaining bone fragments. Pat it dry with a paper towel. Cut off the white parts that remain from the connective tissue and the fattier parts. Slice it thinly and pound it flat.
Season with salt, pepper, and oregano. Pre-cook both sides in a grill pan with a little olive oil.
Place the pre-cooked chicken breast slices in a heatproof dish. Place a slice of ham on top of each one. Thinly slice the apple and spread it evenly over the surface of the ham, then top with sliced cheese.
Bake in a preheated oven for about 20 minutes, or until the top is golden brown. After turning off the oven, leave it inside for another 10 minutes to make it crumbly.