Preheat Oven:
Preheat oven to 400°F (200°C). Lightly grease a 9×13-inch baking dish.

Cook the Beef Mixture:
In a large skillet over medium heat, cook ground beef and chopped onion until beef is browned. Drain excess grease.
Add garlic and cook for another minute. Stir in ketchup, mustard, diced tomatoes, salt, and pepper. Simmer for 3–4 minutes. Remove from heat and stir in 1 cup of shredded cheese.

Assemble the Casserole:
Spread the beef mixture evenly in the prepared baking dish. Top with frozen French fries in a single layer.

Bake:
Bake uncovered for 25–30 minutes, or until fries are golden and crispy.

Add Final Cheese:
Sprinkle remaining 1 cup of cheese over the top. Return to the oven and bake for another 5–7 minutes, or until cheese is melted and bubbly.

Serve:
Top with pickles, green onions, crumbled bacon, or a drizzle of ranch if desired. Serve hot and dig into the madness!