Preheat oven to 375°.
In small skillet heat oil, add onion and sauté until tender, add mushrooms and ¼ teaspoon salt. Heat about 2 minutes until mushrooms are heated through. Set aside.
In a small bowl, combine pumpkin, half and half, sage, pepper, and remaining ¼ teaspoon salt.
Spread ½ cup pumpkin sauce in an 11 X 7 inch baking dish lightly coated with cooking spray.
Top with 3 noodles (noodles will overlap slightly). Spread ½ cup pumpkin sauce to edges of noodles. Top with half of mushroom mixture, ½ cup ricotta cheese, ½ cup mozzarella and ¼ cup Parmesan cheese. Repeat layers. Top with remaining noodles and pumpkin sauce.
Cover and bake in preheated oven for 45 minutes. Uncover; sprinkle with remaining Parmesan cheese. Bake 10-15 minutes longer or until cheese is melted. Let stand for 10 minutes before cutting.