Bring a large pot of salted water to a boil. Add the noodles and cook until just al-dente. Drain and rinse with cold water. Set aside.
Heat olive oil in a large saucepan over medium heat. Add onion and cook until translucent. Add in italian seasoning, red pepper flakes and garlic clove. Cook for 30 seconds and add in the spinach, zucchini and peas. Cook for 10 minutes until spinach is wilted, peas are cooked through and zucchini is tender. Remove from heat and drain off any water.
In a separate bowl combine the ricotta cheeses and grated nutmeg.
Preheat oven to 375 degrees F. Spread 3/4 cup sauce on the bottom of a 9×13″ glass pan. Layer with 4 of the lasagna noodles (3 vertical, one horizontal). Spread on 1/2 of the ricotta mixture and 1/2 of the vegetable mixture. Spoon on 1 1/2 cups of the tomato sauce on top. Continue to layer with lasagna noodles, rest of the ricotta mixture, remaining vegetable mixture and 1 1/2 cups tomato sauce. Top with 4 additional lasagna noodles and remaining 1 1/4 cup tomato sauce. Top with mozzarella cheese and cover loosely with foil.
Bake for 40 minutes. Remove foil and cook for an additional 10 minutes until bubbly and hot.
I like my lasagna pretty saucy! Feel free to cut back to 4 cups of marinara sauce if you’d prefer. For my dairy-free friends, this one is easily adaptable: swap in tofu ricotta for the filling and omit the cheese or use dairy-free mozzarella on top.