In a bowl, combine the ricotta cheese, eggs, Parmesan cheese and spinach; set aside.
Spread one-half of marinara sauce into a greased 2-1/2 quart baking dish; cover with one-half of the spinach mixture and one-half of the sausage.
Sprinkle with one-half of the mozzarella cheese.
Bake, uncovered, at 375°F for 30-35 minutes.
Let stand 5 minutes before serving.