To a large pot of salted boiling water, add your lasagna noodles. Cook until al dente and according to package directions (usually about 7 minutes). Drain and rinse with cool water to prevent cooking. Drizzle with oil to prevent sticking and gently toss to coat.
Heat oil in a large pan over medium heat. Once hot, add the onions and a sprinkle of salt. Sauté until softened and lightly golden. About 5-6 minutes
Add garlic, parsley, oregano, and crushed red pepper then sauté for 30-60 seconds until fragrant.
Add mushrooms and cook until they have released their liquid, reduced their size, and are lightly golden (the pan should be almost dry). About 7-9 minutes.
Now add the spinach and a sprinkle of salt and pepper. You want to cook it until the liquid is released and cooked off. The spinach will reduce in size quite a bit too. About 5-6 minutes. Remove from heat. Taste for seasoning and add if needed
Assembly (*step-by-step photos above)
Add 1 cup of sauce to the bottom ofa9x13 casserole dish, and spread out evenly.
Now add a single layer of lasagna noodles on top of the sauce (5 noodles). I like to overlap them slightly. You will need to cut one of the noodles to fit width-wise.
Now add ½ of the vegan ricotta cheese on top of the noodles and spread it out evenly with a spatula or back of a spoon.
Add ½ of the spinach and mushroom mixture on top of the ricottain an even layer.
Now repeat each step until everything is gone (starting with the sauce, 1 cup for each layer). The last layer of noodles will only have sauce on top. I like to sprinkle it with vegan parmesan cheese. Feel free to leave it plain or top it with homemade vegan mozzarella cheese (or store-bought).
Cover loosely with foil and bake for 30-40 minutes, until heated throughout. Now uncover and bake for 15 minutes to make it crispy and lightly browned on top. * After that, if you want a crispier top, you can turn on the broiler for 2-4 minutes. *Watch carefully so it doesn't burn.
Let the lasagna rest for 15 minutes before cutting. Cut with a knife and remove with a spatula. Enjoy!
Notes
Lasagna Noodles - you'll only need 15 but I make the whole box in case some break apart.
The spinach seems like a lot but it will cook down considerably
Some jarred sauce can be watery which could make your lasagna watery. I prefer homemade or a thick jarred sauce like Rao's Marinara. If your sauce seems watery, you can thicken it up by stirring in 2-3 tablespoons of nutritional yeast and heating it on medium heat for 2-3 minutes. You can also use cornstarch to thicken instead. Make a slurry with 1 tablespoon of cornstarch and 1 tablespoon water. Mix them together and add to the simmering sauce. Whisk well and let cook for 2-3 minutes.
I like my lasagna saucy so I add it generously. Feel free to use less.
Nutritional info includes my vegan ricotta cheese recipe.