1. Preheat oven to 350°. Cook squash in boiling water to cover in a large skillet 8 to 10 minutes or just until tender. Drain well on paper towels.
2. Melt butter in skillet over medium-high heat; add onion, bell pepper, and celery, and sauté 8 to 10 minutes or until vegetables are tender. Remove skillet from heat. Stir in soup and next 4 ingredients. Gently stir in cornbread and squash. Spoon mixture into a lightly greased 13- x-9-inch baking dish.
3. Bake at 350° for 40 to 45 minutes or until golden.
Note: To make ahead, prepare recipe as directed through Step 2. Cover unbaked casserole, and chill up to 24 hours. Let dressing come to room temperature (about 30 minutes), and bake as directed.