In a medium saucepan, melt butter over medium heat; add flour and reduce heat to low, stirring to form a roux.
Stir in milk gradually, blending so that sauce is smooth.
Mix in onion powder, garlic, basil, parsley, oregano, and Parmesan cheese; stir and cook until mixture thickens; season to taste with salt and pepper, then keep warm over low heat, stirring occasionally, while you prepare lasagna.
In lasagna pan or 13 x 9 inch baking pan, spray with non-stick cooking spray or wipe with a little oil and a paper towel.
Spread 3 lasagna noodles across bottom, making sure entire bottom is covered; spread 1/3 of ricotta over noodles.
Place a layer of mushrooms, tomatoes and zucchini over ricotta, and spoon 1/4 of the sauce over the vegetables.
Repeat the layers 2 more times, topping the last cheese/vegetable layer with noodles (there may be a few noodles left over) and the remaining sauce.
Cover and bake for 40 minutes; uncover, sprinkle the top with mozzarella cheese and bake 10-12 minutes more, or until cheese is just starting to turn golden and lasagna is bubbly.
Allow to sit 5-10 minutes before cutting and serving.