Cook Beef:
In a skillet over medium heat, cook ground beef and onions until beef is browned and onions are soft, about 5–7 minutes. Drain excess fat.

Add Seasoning:
Add taco seasoning mix and water to the beef. Stir and simmer for 3–4 minutes until sauce thickens.

Assemble Burritos:
Lay a tortilla flat. Spread about 1/4 cup nacho cheese sauce in the center. Add 1/4 of the beef mixture, a spoonful of cooked rice (if using), diced tomatoes (if using), and sprinkle shredded cheddar cheese on top.

Wrap Burritos:
Fold in the sides and roll the tortilla tightly around the filling.

Melt Cheese:
Heat a non-stick skillet over medium heat and lightly spray with cooking spray. Place burritos seam-side down and cook for 2–3 minutes until golden brown and sealed. Flip and cook another 2 minutes. Pour remaining nacho cheese sauce over the burritos or serve on the side for dipping.

Serve:
Slice in half if desired and serve hot.