Cover with a lid and cook for 2 to 3 min or until the bread is golden brown and the cheese has begun melting. Brush one side of the remaining slices of bread with olive oil. Place the bread, oiled side up, on top of the stacks of bread, tomato, mozzarella, and spinach heating in the skillet, and flip the sandwiches. Cook for another 2 to 3 min until the bread has a chance to turn golden brown and the cheese melts completely. Eat as is, or, if you like, serve with a side of marinara for dipping. Enjoy!