Baked Tortellini Casserole: 2

Baked Tortellini Casserole: 2 tablespoons of olive oil 1 lb ground beef Small yellow onion, diced 2 garlic cloves, minced 1 28oz can of crushed tomatoes, or whole peeled tomatoes crushed by hand 1 8 oz can of tomato sauce 1 teaspoon of kosher salt Freshly ground black pepper to taste 1 24 oz package of fresh cheese tortellini 3 cups of freshly grated mozzarella cheese