Bring a large pot of lightly salted water to a boil. Add pasta and cook according to package directions; drain. Adjust oven rack to the highest position and turn oven on to Broil. Generously butter or grease an 8x8 inch baking dish.
Bring marinara and Alfredo sauces along with spinach and 1 tablespoon of Italian seasoning to a simmer over medium-high heat. Reduce heat to medium-low, and simmer for 10 minutes. Stir cooked tortellini into sauce, then pour into prepared baking dish. Sprinkle with Mozzarella cheese, Parmesan cheese, and remaining 1 teaspoon Italian seasoning.
Broil for a minute or two until cheese has melted and turned golden brown.