In a medium microwave-safe bowl combine squash and 2 tablespoons water; cover with vented plastic wrap. Microwave on high for 4 minutes; stir. Microwave, covered, about 4 more minutes or until squash is tender. Carefully remove plastic wrap. Mash squash; set aside.

Cook pasta according to package directions; drain.

In a medium saucepan, heat butter over medium heat. Add mushrooms and green onions. Cook until tender, about 5 minutes.

Sprinkle flour over mushroom mixture. Cook and stir for 1 minute.

Add milk, salt, pepper and cayenne pepper, if using. Cook and stir over medium heat until thickened and bubbly. Remove from heat.

In another bowl, add pasta, squash and sauce; gently fold to combine.

Transfer half of the pasta mixture to a 2-quart baking dish coated with non-stick cooking spray. Sprinkle with half of the cheese. Add remaining pasta/squash mixture and the rest of the cheese.

Top with bacon and additional sliced green onions.

Bake uncovered for 20-25 minutes at 350 degrees until heated through and cheese is melted.

Serve and season with additional salt and pepper if desired.