8 ounces uncooked spaghetti, broken into 3-inch pieces
3 cups cubed cooked chicken
1 can (10-3/4 ounces) condensed cream of chicken soup, undiluted
1 medium onion, chopped
1 cup 2% milk
1 cup shredded sharp cheddar cheese, divided
1 cup shredded Swiss cheese, divided
1 can (4 ounces) mushroom stems and pieces, drained
1/2 cup chopped roasted sweet red peppers
3 tablespoons mayonnaise
1-1/2 teaspoons steak seasoning
1/2 teaspoon dried basil
Cook spaghetti according to package directions. Meanwhile, in a large bowl, combine the chicken, soup, onion, milk, 1/2 cup cheddar cheese, 1/2 cup Swiss cheese, mushrooms, peppers, mayonnaise, steak seasoning and basil.
Drain spaghetti. Add to chicken mixture; toss to coat. Transfer to a greased 13x9-in. baking dish. Cover and bake at 350° for 20 minutes. Uncover; sprinkle with remaining cheeses. Bake until heated through and cheese is melted, 5-10 minutes longer.
Freeze option: Cover and freeze unbaked casserole. To use, partially thaw in refrigerator overnight. Remove from refrigerator 30 minutes before baking. Bake as directed, increasing time as needed to heat through.