Begin by spreading 1 tablespoon of marinara sauce on one side of each slice of sourdough bread.
On two of the slices (the sauce side), layer 1/2 cup of shredded mozzarella cheese evenly.
Add your choice of toppings on top of the cheese, arranging them evenly, and sprinkle Italian seasoning over the toppings.
Top with the remaining slices of bread, sauce side facing down, so that you have two sandwiches prepared.
In a large skillet, melt 1 tablespoon of butter over medium heat.
Place one sandwich in the skillet and cook until the bread is golden brown and the cheese begins to melt, approximately 3-4 minutes.
Carefully flip the sandwich using a spatula, adding the remaining tablespoon of butter to the skillet if needed. Cook for another 3-4 minutes until golden brown and the cheese is fully melted.
Remove the sandwich from the skillet and repeat with the second sandwich.
Once both sandwiches are cooked, cut them diagonally and serve with extra marinara sauce for dipping.