Preheat the oven to 400°F (204°C). Lightly grease a 9×13-inch baking dish and set aside.
Place the ground beef in a large sauté pan over medium-high heat. Cook, breaking it apart with a spoon, until fully browned and no longer pink. Drain excess grease and remove from heat.
Add the Thousand Island dressing, mayonnaise, diced onion, diced pickles, onion powder, garlic powder, salt, and black pepper to the cooked beef. Stir until evenly combined.
Transfer the beef mixture to the prepared baking dish and spread into an even layer.
Sprinkle the shredded cheddar cheese evenly over the beef mixture.
Arrange the frozen tater tots in a single, even layer on top of the cheese.
Bake uncovered for 40–45 minutes, or until the tater tots are golden brown and crispy.
Remove the casserole from the oven. Immediately sprinkle the shredded lettuce over the top and drizzle with additional Thousand Island dressing.
Serve warm.