Use a mandolin to slice each zucchini lengthwise to about 1/8 inch thick. Season slices with kosher salt and allow to sit for 10 minutes.
Blot with a paper towel to remove excess moisture and salt. Arrange slices in a single layer on a lined baking sheet and bake for 10 minutes. Remove from oven and set aside.
In a sauté pan, heat olive oil with a pinch of red pepper flakes and garlic until fragrant, 30-60 seconds.
Add onion and extra diced zucchini if there was any, season with salt. Sauté for about 5 minutes, until starting to soften. Add crimini and shiitake mushrooms, oregano, thyme and season with salt and pepper. Add porcini mushrooms but save the soaking water. Sauté for about 15 minutes, until water is evaporated. Add about 1/4 cup of the porcini soaking water and sauté until that has evaporated and mushroom mixture is browned.
To assemble lasagna, pour about 1/4 cup of marinara sauce in the bottom of a 9x13 baking dish. Layer about half of the zucchini slices on top, cover with half of the mushroom mixture, cover that with about half of the remaining marinara sauce, then sprinkle half of the parmesan cheese and half of the mozzarella cheese. Repeat one time.
Bake until cheese is browned and bubbly, about 40 minutes. If cheese is browning too much, cover with foil. If cheese is not browning enough, finish under the broiler for 1-2 minutes.
Remove from oven and allow to sit for a few minutes before cutting. Serve with chopped basil and more parmesan cheese, if desired.