Step 1

Preheat oven to 350 degrees F.  Coat a 9- x 13-inch casserole dish with cooking spray.

Step 2

Cook spaghetti according to package directions; drain, return to pot, and set aside.

Step 3

Meanwhile, in a large skillet over medium-high heat, melt butter; sauté onion, bell pepper, and mushrooms 6 to 7 minutes, or until tender. Add  vegetable mixture and remaining ingredients to spaghetti; mix well.

Step 4

Place mixture in prepared casserole dish, cover, and cook 25 to 30 minutes, or until heated through.