1. Preheat oven to 450 degrees. Spray a medium sized casserole dish with nonstick cooking spray.
2. In a large skillet over medium heat, cook bacon until crisp. Remove from pan, reserving 1/2 teaspoons dripping in pan. Add onions and cook, stirring frequently, until soft and caramelized. Combine roasted squash, bacon, onions, and cooked pasta and set aside.
3. In a sauce pan, melt butter. Add flour and whisk to combine - cook for about 2 minutes, stirring constantly, but do not brown. Gradually add milk, whisking constantly to remove lumps and heat until sauce begins to thicken. Add garlic powder, salt and pepper. Stir in provolone and Parmesan cheese, cook until cheese is melted and sauce is smooth. Pour over pasta mixture.
3. Spoon pasta into prepared casserole dish. Sprinkle top with additional Parmesan cheese if desired. Bake in preheated oven for 10 minutes until top begins to slightly brown.