Slice onions, chop mushrooms and zucchini into small cubes, and chop spinach. Peel garlic and you will need a garlic press to press it into the pan.
Preheat a large cooking pan over medium heat and add oil. Saute onions first and then add zucchini and mushrooms.
When zucchini and mushrooms have softened, add spinach and garlic to the pan, stir and cook until spinach is wilted. Season the vegetables with salt, pepper, garlic powder, and herbs.
Take vegetables out of the pan and drain off excess juice.
Ricotta Mixture:
Mix all the ingredients for the ricotta layer and set it aside until ready to use.
Assembling Lasagna:
You can use oven-ready lasagna noodles or ones that need to be pre-cooked. If using ones that need to be pre-cooked, boil it while vegetables are cooking. Drain off water and then separate the noodles once cooled enough to be handled. **If layering dry noodles in the lasagna, make sure that sauce touches each layer of pasta so the noodles soak up the moisture.
Lightly grease the 9×13 casserole dish on the bottom and up the sides and spread about a cup of marinara sauce over the bottom of the dish.
Layer lasagna noodles in one even layer and spread cooked vegetables mixture over it.
Add another layer of lasagna noodles over vegetables and spread about cup and a half of sauce over the noodles.
Spoon ricotta mixture all over the sauce and spread it into one even layer. (It’s alright if the sauce gets mixed in a little.)
Top ricotta with another layer of lasagna noodles and spread sauce over the top evenly and generously.
Spread shredded cheese over the top and sprinkle some oregano over the top. Spray a sheet of aluminum foil with some cooking spray and cover the lasagna dish with foil, oiled side down.
Bake lasagna at 350° for 45 minutes. Take off the foil and bake for another 10-15 minutes.