Step 1

Preheat the oven to 375 degrees.

Step 2

Place the meatballs on an aluminum foil-lined baking sheet, and bake for 15-20 minutes, turning once.

Step 3

In the bottom of a 9x13 baking dish or large round pan, mix together the marinara sauce and baby spinach. Place the cooked meatballs in the dish, nestling them down in the sauce. Dot the top of the meatballs with teaspoonfuls of ricotta cheese. Sprinkle all of the mozzarella cheese over the top.

Step 4

Bake at 375 degrees for 30 minutes, until the casserole is bubbly. If desired, you can place the dish under the broiler for an additional 3-4 minutes, until the cheese is starting to brown.