Preheat your oven to 375°F (190°C). Lightly grease your baking dish or spray it with non-stick cooking spray.
In a large skillet over medium heat, add the ground beef and diced onions. Season with garlic powder, onion powder, salt, and pepper. Cook until the beef is browned and fully cooked, and the onions are soft and translucent. Drain any excess fat if necessary.
While the beef cooks, combine the biscuit mix and milk in a bowl. Stir gently just until combined — be careful not to overmix.
Spread the cooked beef and onion mixture evenly in the prepared baking dish. Sprinkle the shredded cheddar cheese over the beef layer. If using turkey bacon, sprinkle the crumbled cooked bacon evenly on top of the cheese. Drop spoonfuls of the biscuit dough over the entire surface, covering as much as you can.
Bake for 20-25 minutes or until the biscuit topping is golden brown and cooked through. The biscuits should be puffed up and nicely browned.
While the bake is in the oven, whisk together the ketchup, mustard, mayonnaise, and relish in a small bowl.
Once baked, remove the casserole from the oven and let it cool for a few minutes. Drizzle the special sauce generously over the top. Serve with optional shredded lettuce and sliced tomatoes.
