Combine the olive oil, garlic and oregano together. Brush on the exterior of all 16 slices of bread.
Layer 4 slices of bread each with 2 slices provolone cheese, 2 tablespoons mozzarella cheese, 1 tablespoon Parmesan cheese, and 4 slices of pepperoni, or other toppings, if using. each. Top with remaining 4 slices of bread.
Heat skillet/griddle to medium heat. Grill sandwiches for 5-6 minutes per side, until golden and cheese is melted.
Bring marinara, oregano, garlic, and stock to a boil and reduce to a simmer. Simmer for 15-20 minutes, allowing flavors to come together.
Serve sandwich with soup.
Pizza Grilled Cheese is best served immediately after preparation. The soup can be store in an airtight container for 3-4 days in the refrigerator. Feel free to use any type of thick bread you like for these sandwiches, even gluten-free bread works great. Mix and match the types of cheeses you have on hand to make these sandwiches. If you don't care for pepperoni, try sliced olives, mushrooms, spinach, or simply make Cheese Pizza Grilled Cheese Sandwiches. Whatever filling you select, be cautious to not overstuff your sandwiches.