Adjust oven racks to upper-middle and lower-middle positions. Heat oven to 400°F (205℃). Line 2 rimmed baking sheets with parchment paper. Arrange bacon slices in a single layer (slightly overlapping if needed) on prepared baking sheets. Bake bacon, switching and rotating baking sheets halfway through, until browned and crisp, 15 to 20 minutes. Use tongs to transfer cooked bacon to a paper towel–lined plate to drain and reserve rendered fat. Heat broiler.

Brush bread slices very lightly on both sides with reserved bacon fat, then arrange on 2 clean baking sheets. Working one baking sheet at a time, broil on the upper-middle rack (about 6-inches from broiler), flipping bread slices halfway through, until bread is light golden brown on both sides, 1 to 2 minutes per side. Set aside.

Sprinkle tomato slices all over with salt and pepper; set aside.

Using a butter knife or offset spatula, spread 1 tablespoon mayonnaise evenly over 1 side of each bread slice. Place 4 prepared bread slices on a clean work surface, mayonnaise side up. Layer 2 cut lettuce leaf halves, 2 tomato slices, 2 cooked bacon slices, and 2 turkey slices—in that order—on the prepared bread slices arranged on the counter. Slightly overlap the ingredients as needed to fit within the parameters of the sandwich bread.

Top the 4 sandwiches with 1 prepared bread slice each, mayonnaise-side down. Press gently to secure. Repeat layering 2 lettuce leaf halves, 2 tomato slices, 2 cooked bacon slices, and 2 turkey slices on top of the bread slices of each prepared sandwich.

Top with the remaining 4 bread slices, mayonnaise side down. Press gently to secure and insert 4 toothpicks into each sandwich, spaced evenly to create 4 quadrants. Use a serrated knife to cut each sandwich on the diagonal to create triangular quarters. Serve.