Preheat the oven to 350°F (175°C). Spray a 6″x9″ casserole dish with non-stick cooking spray.
Arrange the tater tots in an even layer on the bottom of the casserole dish. Par-bake for 20 minutes, then set aside.
While the tater tots bake, spray a frying pan with non-stick spray. Add the ground beef and half the diced onion (reserve the rest for topping). Cook the beef until no longer pink, breaking it apart as it cooks.
Add paprika, garlic powder, onion powder, salt, and mustard to the beef mixture, stirring to combine. Add ¼ cup of water and let it simmer until the water evaporates.
Spread the beef mixture evenly over the par-baked tater tots. Top with shredded cheddar cheese and bake at 350°F (175°C) for 10 minutes, or until the cheese is melted.
While the casserole bakes, combine the mayo, ketchup, diced pickles, and white vinegar to make the sauce.
Once the casserole is done, drizzle with the sauce and top with shredded iceberg lettuce, sliced tomato, the remaining raw onion, and pickle slices. Sprinkle sesame seeds on top for a finishing touch.