1. Preheat oven to 350°. Cook squash in boiling water to cover 8 minutes or until tender. Drain well, and press gently between paper towels to remove excess moisture.
2. Melt butter in a large skillet over medium-high heat; add onion, and sauté 3 to 5 minutes or until tender.
3. Stir together onion mixture, soup, and next 4 ingredients in a large bowl. Stir in squash and breadcrumbs. Spoon mixture into a lightly greased 13- x 9-inch baking dish. Sprinkle with cheese, and bake at 350° for 30 minutes or until lightly browned.