Heat a pot of salted water to a boil, then add the pasta shells. Cook until just tender, drain and rinse under cold water.

While the shells are cooking, heat a large non stick pan on medium high heat, add the ground beef and onion, cook, breaking up the meat with your spatula, until the beef is no longer pink.

Drain the fat then mix in the tomato sauce, ketchup, mustard, and pepper. Stir together.

Add 3/4 cup of the cheese. Stir the cheese in.

Preheat your oven to 180 C (350 F) and grease a 7x11 baking dish. Use a teaspoon and fill each shell and arrange in the baking dish until all the shells and filling is used.

Bake uncovered for 15 minutes. Sprinkle with remaining cheese and bake for another 5 minutes or until the cheese is melted.

Optionally, squirt some ketchup over the shells.

Serve and enjoy. Add chopped pickles, chopped tomatoes, or shredded lettuce as desired.