Preheat the oven to 400°F. Lightly grease a 9x13-inch baking dish.

In a large skillet over medium-high heat, cook the ground beef, diced onion, and All Purpose Seasoning, breaking up the meat as it cooks. Continue cooking for 6 to 7 minutes, or until the beef is browned and no pink remains. Drain any excess grease.

In a mixing bowl, whisk together the mayonnaise, relish, Dijon mustard, white vinegar, garlic powder, onion powder, and paprika until smooth.

Reserve ⅓ cup of the Big Mac Sauce for serving. Stir the remaining sauce into the cooked beef mixture until evenly combined.

Transfer the beef mixture to the prepared baking dish and spread into an even layer.

Sprinkle the cheddar cheese blend evenly over the beef mixture.

Arrange the frozen tater tots in a single layer over the cheese.

Bake for 40 to 45 minutes, or until the tater tots are golden brown and crispy and the casserole is bubbling around the edges.

Remove the casserole from the oven and let it rest for 5 minutes.

Top with shredded lettuce, chopped tomatoes, and chopped pickles. Drizzle with the reserved sauce and sprinkle with sesame seeds before serving.