In a skillet over medium heat, cook the bacon until crispy. Remove and drain on paper towels. Reserve a tablespoon of bacon grease in the skillet.
Spread 1 tablespoon of mayonnaise on one side of each slice of bread.
Heat the skillet with the reserved bacon grease over medium heat. Place 4 slices of bread, mayonnaise side down, in the skillet.
Layer each slice of bread with 1 ounce of cheddar cheese, 1 ounce of mozzarella cheese, 2 slices of bacon, a few tomato slices, and a couple of lettuce leaves. Season with salt and pepper.
Top with the remaining slices of bread, mayonnaise side up. Cook until the bottom is golden brown, about 3-4 minutes.
Carefully flip the sandwiches and cook the other side until golden brown and the cheese is melted, about 3-4 minutes more.
Remove from the skillet, slice in half, and serve immediately.