Cheeseburger Stuffed Shells

Large shells (1 lb)

Olive oil (2 tbsp)

Onion (chopped, 1/2 cup)

Garlic (minced, 2 tbsp)

Ground beef (1 lb)

Pettie diced tomatoes (15 oz (or 1 can))

Ketchup (1/4 cup)

Mustard (3 tsbp)

Cheddar cheese (shredded, 1 cup (divided))