In a mixing bowl, combine the lean ground beef, Romano cheese, panko bread crumbs, minced garlic, dried basil, dried parsley, crushed red pepper flakes, salt, and pepper. Mix until just combined; be careful not to overmix.
Using your hands, form the mixture into small meatballs, about 1 inch in diameter.
Heat olive oil in a skillet over medium heat. Add the meatballs and cook for about 5-7 minutes, turning occasionally until browned and cooked through. Remove from skillet and set aside.
In the same skillet, add the can of diced tomatoes. Simmer for a few minutes until heated through.
Butter one side of each slice of bread. On the unbuttered side of two slices, layer the Fontina cheese, cooked mini meatballs, a spoonful of tomato sauce, and then top with Provolone cheese. Place the remaining slices of bread on top, buttered side facing out.
In the skillet, cook the sandwiches over medium heat for about 4-5 minutes on each side, or until the bread is golden brown and the cheese is melted.
Remove the sandwiches from the skillet, slice them in half, and serve with extra tomato sauce for dipping.
