Preheat the oven to 400 degrees F. Lightly spray a 8-by-8 baking dish with olive oil spray.
Place the spinach in the middle of a clean dishtowel. Fold up the towel over the spinach and wring out as much moisture as possible. Put the spinach in a large mixing bowl.
Add the ricotta, Parmesan, egg whites, garlic powder and nutmeg. Stir well.
Move spinach mixture to the prepared dish. With the back of a spoon, spread it out to uniformly fill the dish. Bake for 20 minutes, or until is hot throughout and the top begins to brown. Let stand for five minutes to slightly cool.
Place the sauce in a microwaveable bowl. Microwave on low power for 15-second intervals until warm. Cut the spinach-ricotta bake into 6 equal pieces, transferring each piece to a serving plate. Spoon 1/4 cup of sauce over each serving. Serve immediately.