1 can (10-3/4 ounces) reduced-fat reduced-sodium condensed cream of mushroom soup, undiluted
1 cup sliced fresh mushrooms
1 cup shredded reduced-fat cheddar cheese
1 cup fat-free milk
1 can (5 ounces) light water-packed tuna, drained and flaked
2 tablespoons diced pimientos
3 teaspoons dried minced onion
1 teaspoon ground mustard
1/4 teaspoon salt
1/3 cup crushed cornflakes
Cook macaroni according to package directions. Meanwhile, in a large bowl, combine the soup, mushrooms, cheese, milk, tuna, pimientos, onion, mustard and salt. Drain macaroni; add to tuna mixture and mix well.
Transfer to a 2-qt. baking dish coated with cooking spray. Sprinkle with cornflakes. Bake, uncovered, at 350° for 25-30 minutes or until bubbly. Freeze option: Cool unbaked casserole before topping with cornflakes; cover and freeze. To use, partially thaw in refrigerator overnight. Remove from refrigerator 30 minutes before baking. Preheat oven to 350°. Top casserole with cornflakes and bake as directed; increase time as necessary to heat through and for a thermometer inserted in center to read 165°.