Heat a skillet over medium heat. Add the sliced zucchini and cook for 8–10 minutes until tender and golden. Remove and add spinach, cooking until wilted, about 3–4 minutes.

In a medium bowl, combine ricotta, Parmesan, beaten egg, minced garlic, basil, and parsley. Mix in cooked spinach and season with salt, pepper, and crushed red pepper.

In a baking dish, spread ½ cup of marinara sauce on the bottom. Layer noodles, zucchini strips, half of the cheese mixture, and sprinkle with mozzarella. Repeat layers, topping with remaining noodles, marinara, and cheese.

Preheat oven to 350°F (175°C). Cover the baking dish with foil and bake for 30 minutes. Remove foil and cool for 15 minutes before slicing.