Preheat oven to 400F (200C) and coat a 9x13 inch baking dish with non-stick spray.
In a large skillet over medium-high heat, brown the ground beef until fully cooked, then drain any excess moisture.
Season the beef with salt, pepper, and onion powder.
In a small mixing bowl, whisk together light mayonnaise, sugar-free ketchup, mustard, pickle juice, and smoked paprika to create the special sauce.
Spread the steamed and dried cauliflower florets evenly across the bottom of the prepared baking dish.
Layer the seasoned beef over the cauliflower, followed by the diced onions and chopped pickles.
Drizzle half of the prepared special sauce over the beef mixture.
Distribute the shredded cheddar cheese evenly over the top.
Bake for 20 to 25 minutes until the cheese is melted and the edges are bubbling.
Remove from oven and let stand for 5 minutes.
Top with shredded iceberg lettuce, the remaining special sauce, and sesame seeds before serving.