Preheat the oven to 350 degrees F. Spray a 9x13-inch baking dish with non-stick spray. Place a large skillet over medium heat and add the butter, onions, mushrooms, and garlic. Saute for 5-10 minutes, stirring occasionally, then add the sherry and cook until all the liquid has absorbed.
Meanwhile mix the ricotta cheese with the dried thyme, oregano, garlic powder, crushed red pepper, 1 teaspoon of salt, and 1/2 teaspoon of black pepper. Then once the mushrooms are cooked, scoop them out of the skillet and add the zucchini slices to sear quickly, about one minute per side.
Place 4 lasagna noodles in the bottom of the baking dish, followed by the arugula, one-third of the ricotta, and one third of the mozzarella. Then add another layer of 4 lasagna noodles and top with the mushroom mixture. Cover with one-third of the ricotta and one-third of the mozzarella. Add a final layer of 4 lasagna noodles and top with the seared zucchini slices. Then cover with the remaining ricotta, mozzarella, and the Parmesan cheese.
Cover with foil and bake for 30 minutes. Then uncover and move to the top rack. Bake another 5-10 minutes until the cheese on top starts to get a little crispy. Allow the vegetable lasagna to rest at least 15 minutes, then cut and serve warm.