Heat the oven to 375°F (190°C). Lightly grease a 9 × 13-inch baking dish with cooking spray or oil.
Cook the ground beef in a large skillet over medium-high heat for 7 to 9 minutes, breaking it into small crumbles. Cook until no pink remains and the beef reaches 160°F (71°C). Drain excess grease.
Reduce the heat to medium-low. Stir in the salt, pepper, garlic powder, onion powder, Worcestershire sauce, 2 tablespoons ketchup, and 1 tablespoon mustard. Cook for 1 to 2 minutes.
Stir the mayonnaise, 2 tablespoons ketchup, 1 tablespoon mustard, finely chopped pickles, pickle juice, and paprika together until smooth. Refrigerate while the casserole cooks.
Transfer the seasoned beef to the prepared baking dish and spread it into an even layer.
Scatter 2 cups shredded cheddar evenly over the beef without pressing it down.
Bake uncovered for 15 to 18 minutes, until the cheese is fully melted and the edges are bubbling. Broil for 1 to 2 minutes if you want a lightly browned top.
Scatter the chopped pickles and diced onion over the hot casserole. Add shredded lettuce, drizzle with the chilled burger sauce, and finish with sesame seeds if using.
Leave the casserole on the counter for 5 minutes before cutting or scooping into portions.
