Prepare the egg. Crack one egg into a small bowl and set aside.
Heat the skillet. Add a little olive oil to a nonstick skillet over medium heat. Brush evenly over the bottom.
Make the cheese ring. Add 50 g of shredded mozzarella cheese. Use a spatula to arrange it into a ring, leaving enough space in the center for the egg.
Add the egg and ham. Carefully pour the egg into the center of the cheese ring. Season with salt and black pepper, then place three slices of ham over the egg.
Add the bread. Place one slice of bread on top. As the mozzarella melts, use a spatula to fold the cheese around the four edges of the bread.
Flip the sandwich. Lightly brush the bread with olive oil. Once the bottom is golden brown and the egg is set enough to flip safely, carefully turn it over.
Add the fillings. Spread about 1 tablespoon of mayonnaise on top. Add a lettuce leaf, a tomato slice, a little salt and black pepper, and one slice of cheese.
Finish the sandwich. Cover with the second slice of bread and lightly brush the top with olive oil. Cook over medium heat for about 2 minutes, then flip and cook for another 2 minutes, until golden brown and the egg is fully cooked.
Serve. Transfer to a plate and enjoy your crispy, cheesy egg breakfast sandwich while warm!