Sausage Casserole - Freezes easily

Freezes really well.....
1 lb sweet hot Italian sausage- ground
1 medium onion, chopped
3 cloves garlic - minced
2 26oz jars marinara sauce
6 Tbsp bottled basil pesto
1 lb penne pasta
1/2 lb mozzarella cheese
1 Cup parmesan cheese1
bag (6 oz) spinach (frozen, thawed, works fine)

In large non-stick skillet, cook sausage on medium-high heat,breaking up meat, until meat no longer is pink, 5 minutes. Add onion,stirring constantly until onion is softened, about 5 minutes. Addgarlic, cook 1 minute. Add marinara sauce, simmer over medium heat 10minutes. Stir in pesto. Set aside.2. Cook penne according to package directions3. Heat oven to 375. Coat 13x9 dish with non-stick cooking spray. Spreadthin layer of sauce over bottom of dish.4. In large bowl, combine cooked penne, remaining sauce, cheese, 3/4 Cparmesan and the spinach. Spoon into baking dish. Sprinkle the remainingparmesan over the top.5. Bake at 375 for 30 minutes