Cook the lasagna according to the package directions; drain. Preheat the oven to 350°F.
In a large skillet, heat the olive oil over medium heat. Add the onion, garlic, and mushrooms, and sauté for 2 to 3 minutes, or until the onion is tender.
Add the Steamin’ Greens and reduce the heat to medium-low; cover, and cook for 10 minutes, or until the vegetables are tender.
Stir in the nutmeg, salt, and pepper.
Meanwhile, in a medium bowl, combine the Alfredo sauce, ricotta cheese, 1/2 cup mozzarella cheese, and 1/2 cup Parmesan cheese; mix well.
In a 9 x 13 baking dish, layer one-third of the sauce mixture, 3 noodles then one-third of the vegetable mixture and one-third of the sliced tomatoes. Repeat the layers 2 more times, ending with sliced tomatoes. Cover with aluminum foil and bake for 1 hour.
Remove from the oven and uncover; sprinkle the remaining 1/2 cup Parmesan cheese and 1 cup mozzarella cheese over the top and bake uncovered for 5 minutes, or until the cheese is melted.