Mix softened butter with grated parmesan and garlic powder until smooth. Spread this mixture evenly on the outer sides of each bread slice for extra crispness and flavor.
Lay cheese slices on the inside of the bread first, then stack your deli meats, finishing with another layer of cheese. This helps everything melt together perfectly.
Heat a skillet over low to medium heat and grill the sandwiches slowly. Flip once the first side becomes golden so the cheese melts completely before the bread browns too much.
In a bowl, whisk mayonnaise, vinegar, Italian seasoning, parmesan, and pepper. Toss shredded lettuce, onion, and banana peppers in the dressing until evenly coated.
Once grilled, carefully open the sandwiches and add a generous layer of dressed salad and optional tomato slices. Close gently to keep fillings in place.
Cut each sandwich diagonally and serve immediately while warm and crispy for the best eating experience.