Preheat the oven to 400°F (200°C) and grease a large baking dish.
Cook ground beef and diced onion in a skillet over medium heat until browned, then drain excess fat.
Add minced garlic, salt, pepper, paprika, onion powder, garlic powder, Worcestershire sauce, ketchup, mustard (if using), and pickle relish to the beef. Stir and simmer for 2 to 3 minutes.
Spread the beef mixture evenly in the prepared baking dish.
Sprinkle shredded mozzarella and cheddar cheese evenly over the beef layer.
Arrange the frozen French fries in a single layer on top of the cheese.
Optionally, sprinkle cooked bacon bits over the fries.
Bake uncovered for 30 to 35 minutes until fries are golden and crispy.
Remove from oven and let rest for 5 minutes.
Garnish with chopped parsley or green onions before serving.
Serve with extra ketchup, burger sauce, ranch, or spicy mayo on the side.