Preheat oven to 400 degrees. Place zucchini and squash chunks in colander with salt for 15 minutes to remove some of the water. Toss zucchini, squash, pepper and onion with salt, pepper, garlic powder, Italian seasoning, and olive oil to coat vegetables. Then roast at 400 degrees for about 10-15 minutes, or until slightly soft.
Reduce oven to 375 degrees if baking casserole immediately.
Sauté mushrooms in olive oil until starting to brown, then remove from pan and drain. Mix all cooked vegetables, pasta, red pepper flakes, and crushed tomatoes in a large bowl. Then stir in spinach. Taste and adjust seasonings as desired.
Layer veggie pasta mixture with ricotta and parmesan in a casserole pan. Top with mozzarella.
Bake uncovered at 375 degrees for 25-35 minutes or until cheese is melted and casserole is heated through.