Preheat your oven to 400°F (200°C) and spray a large baking dish with nonstick cooking spray.

In a skillet over medium heat, brown the ground beef until fully cooked. Drain any excess fat and add diced onions; sauté until translucent.

Stir in ketchup and mustard until well combined.

Layer half of the frozen fries in the prepared dish, followed by half of the beef mixture and half of the cheddar cheese. Repeat layering.

Bake for 25-30 minutes or until golden brown and bubbly.

Let cool for a few minutes before serving.