Preheat the oven to 400º F.
Slice the zucchini lengthwise as thin or thick as you'd like. Set aside. Salt the zucchini and let it sit for a few minutes. The salt brings out some of the moisture of the zucchini. Pat dry with paper towels.
Sauté onions in a fry pan until translucent using olive oil or a little veggie broth.
Add the plant-based meat (or ground beef) to the pan. Mix with the onions over medium-high heat. Break down into fine pieces with a spatula. Pan-cook until browned and no longer pink.
If you are adding chopped mushrooms, add them now. Mix well with meat and onions and simmer for about five minutes.
Pour the marinara sauce on top of the beef (reserve 1/2 cup) and stir together, then remove from heat.
In a medium bowl, make the non-dairy cashew ricotta (recipe provided) or use a dairy version. Stir the ricotta cheese of your choice, parmesan, egg, and salt and pepper together.
Spread 1/2 cup of marinara sauce into the bottom of your 9x13" casserole dish.
Add your zucchini slices on top of the sauce. They can overlap, or you can place them side-by-side.
Top the zucchini with 1/2 of the meat sauce and evenly spread 1/2 the ricotta mix on top of that.
Add 1/2 cup of grated mozzarella over the ricotta, along with a sprinkle of chopped parsley and basil.
Repeat to create the same layers one more time.
Top the lasagna with a final layer of zucchini slices, ricotta cheese, a sprinkle of chopped parsley and basil, and the remaining 1/2 cup mozzarella cheese.
Place the lasagna in the oven and cook for 40-45 minutes. Broil for a couple of minutes at the end to get a nice, golden top.
Garnish with basil leaves, whole or chopped, and serve.