Preheat a skillet or griddle over medium heat.
Spread olive oil on one side of each bread slice.
Place two slices of bread, oil-side down, in the skillet.
Spread marinara sauce evenly on each slice of bread.
Add shredded mozzarella and any other toppings on top of the sauce.
Top with the remaining slices of bread, oil-side up.
Cook for about 4-5 minutes until golden brown.
Carefully flip the sandwich using a spatula.
Once both sides are golden and the cheese has melted, remove from heat.
Slice and serve with additional marinara on the side.