Preheat the oven to 375°F (190°C).
Prepare the vegan ricotta according to your recipe or use a prepared batch; set aside.
Dice the mushrooms and zucchini.
In a large skillet over medium-high heat, sauté the mushrooms for about 3 minutes using 1–3 tablespoons water or vegetable broth for an oil-free method, adding more liquid as needed.
Add the diced zucchini to the skillet and cook for about 5 minutes, stirring occasionally.
Add the baby spinach and stir for about 1 minute until slightly wilted; remove from heat and set the vegetable mixture aside.
Spread 1.5 cups of marinara sauce on the bottom of a deep 9" x 13" casserole dish.
Place 4 no-boil lasagna noodles over the sauce.
Dot half of the vegan ricotta across the noodles in small spoonfuls, then spread half of the sautéed vegetables over the ricotta, and pour 1.5 cups marinara over the layer.
Place 4 more noodles, then add the remaining ricotta and remaining vegetables, then 1.5 cups marinara.
Finish with the last 4 noodles and top with the final 1.5 cups of marinara, ensuring noodles are fully covered with sauce.
Cover the dish with foil and bake for 45 minutes, then remove the foil and bake uncovered for an additional 10–15 minutes.
Let the lasagna rest for 10 minutes before slicing and serving.
