Slices of butternut squash stand in for noodles in this veggie-packed lasagna with spinach, mushrooms and a creamy parmesan cheese sauce. You can make the parmesan cheese sauce with regular flour or swap in gluten-free flour to make this dish gluten-free. Look for a squash with a long, straight neck for the best results. Serve with a green salad for a vegetarian meal that you'd be happy to serve to company.