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)
To a 9x13 casserole dish,add a layer of sauce to the bottom 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). 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.