Prepare all ingredients, ensuring they are readily accessible.

Preheat the oven to 375°F (190°C). Coat a 9x5-inch loaf pan with cooking spray for easy removal.

In a mixing bowl, combine the ground beef, stuffing mix, chopped onion, and egg. Mix by hand until fully integrated. Press this mixture evenly into the prepared loaf pan.

Place the pan in the preheated oven and bake for 35 to 40 minutes, or until the meatloaf is no longer pink in the center. Use an instant-read thermometer to confirm it has reached an internal temperature of at least 160°F (70°C).

Sprinkle shredded mozzarella over the top of the meatloaf and allow it to rest for approximately 10 minutes, letting the cheese melt to create a creamy finish.

Recipe Tip: For convenient individual servings, divide the mixture among four mini loaf pans. Bake at 375°F (190°C) until each loaf reaches an internal temperature of at least 160°F (70°C), approximately 25 to 30 minutes.