Kerri's Tuna Casserole

1 (7 oz.) Pkg. (1 ½ cups) uncooked elbow macaroni
1 cup milk
4 oz. (1 cup) shredded Cheddar cheese
1 (10 3/4 oz.) can condensed cream of mushroom soup
1 (5 oz.) can tuna, drained, flaked
1 (4 oz.) Can mushroom pieces and stems, drained (optional)
1 (2 oz.) Jar chopped pimientos (optional)
2 teaspoons instant minced onion
½ teaspoon dry mustard
½ cup crushed potato chips or bread crumbs
Heat oven to 350 degrees. Grease 2-quart casserole. In large saucepan or dutch oven, cook macaroni to desired doneness as directed on package. Drain; return to saucepan. Add all remaining ingredients except potato chips; stir to combine. Pour mixture into greased casserole. Sprinkle with potato chips or bread crumbs. Bake at 350 degrees for 25 to 35 minutes or until thoroughly heated. Makes 6 (1 1/4 cup) servings.