Spread ½ a tablespoon of mayo on one side of each slice of bread. Heat a cast iron pan or a griddle over medium-low heat. Once the pan has heated, place one slice of bread mayo side down, lay 2 pieces of cheese over the bread, 3 pieces of bacon torn in half, and 2 more slices of cheese on top of that. Lay the other slice of bread mayo side up on top.

Cook for 3-4 minutes on each side until nicely golden brown and crispy, flip the grilled cheese over and cook for another 3-4 minutes. Set aside and repeat with the other bread and cheeses. Sprinkle both sides of the grilled cheese with the grated parmesan cheese. Serve hot with tomato soup, and enjoy!