Preheat your oven to 350°F.
Cook your diced onion and ground beef over medium heat in a large nonstick skillet, until the onions are soft and the beef is cooked through.
Drain the grease from the pan. Season with salt and pepper, and mix in your special sauce.
Grab a large casserole dish or rectangle pan. You'll want it to hold about 3 quarts. A classic 8x9 baking dish will work.
Layer your potatoes, pepper, pickles, and tomatoes in to the pan. Season with a little bit of salt and pepper.
Top your veggies with the beef and onion mixture. Sprinkle it with the sesame seeds, then give it all a big stir to combine. You want everything to be evenly layered in the dish.
Cover the dish with your casserole cover or some aluminum foil, and bake it for 1 hour. You want the potatoes to be soft, but not mushy.
Let the casserole sit for about 10 minutes, then garnish it with the lettuce, tomatoes, pickles, onions, sesame seeds, and a drizzle of special sauce.