Divide ground beef into 4 patties, sprinkle with salt and black pepper, and set aside.
Place bacon in a large skillet and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain the bacon slices on paper towels and keep warm. Cook onion in the bacon drippings until lightly browned, about 10 minutes, stirring often; sprinkle with sugar during frying if desired. Set onion aside.
Set oven rack about 6 inches from the heat source and preheat the oven's broiler.
Open hamburger buns and place onto a baking sheet with cut sides up; toast under the broiler until browned, 1 to 2 minutes. Set buns aside.
Pan fry ground beef patties in the same skillet as onions until browned and the juices run clear, 5 to 8 minutes per side. An instant-read meat thermometer inserted into the center of a burger should read at least 160 degrees F (70 degrees C). Place a slice of Cheddar cheese onto each patty and allow cheese to melt.
To assemble, spread peanut butter onto bottom halves of buns; spread ketchup onto top halves. Top the peanut butter with pickle slices, cooked onion, burgers with cheese, a slice of bacon, several tomato slices, and about 1/4 cup shredded lettuce per sandwich.
