Polenta Sausage Mozzarella Casserole

Name: Polenta Sausage Mozzarella Casserole
Ingredients: 4 tablespoons extra virgin olive oil; 1 28-ounce can crushed tomatoes; 1 tablespoon chopped fresh oregano; 1 yellow onion, chopped; 4 cloves garlic, minced; 1/2 teaspoon salt; 1/2 teaspoon freshly ground black pepper; 1 teaspoon fennel seeds; 1 pound sweet Italian sausage (removed from casings); 2 pounds of prepared polenta, 1/2-inch slices if using prepared polenta in a tube (can use one recipe of creamy polenta , leave out the cream cheese); 1/2 pound (8 ounces) fresh mozzarella, sliced into 1/4-inch slices