In a very large bowl, mix together cooked pasta, cream of chicken soup, tuna, water chestnuts, peas (no need to thaw them first), and 1 cup of the cheese. Mix until everything is combined.
2 cans (10 ¾ oz.) cream of chicken soup, 2 cans (5 oz.) solid white albacore tuna in water, drained, 1 can (5 oz.) sliced water chestnuts, drained and roughly chopped, 2 cups frozen peas, 1 ½ cups grated sharp cheddar cheese, divided
Spread casserole mixture into prepared pan. Sprinkle with remaining cheddar cheese or top with optional topping (see notes).
Bake for 35 minutes or until golden brown and heated through. If noodles are getting too crispy for your liking, cover with foil.
Video
Notes
If you like, stir in ¼ cup finely minced onions.
Optional toppings: Crushed potato chips, canned fried onions, crushed Ritz crackers or bread crumbs mixed with melted butter and cheese. Top casserole with desired topping before baking, bake as directed.
Make ahead: Bake one now, freeze one to eat later. Divide the mixture evenly between two baking dishes. Bake one today, and freeze the other casserole, wrapped and labeled, to eat later. For best results, thaw overnight in the refrigerator before baking as directed.
Troubleshooting: Try stirring a half cup of milk into the mixture before baking if your casserole consistently turns out dry. If you prefer, cover the casserole with foil to prevent the top from drying out. If you added toppings, uncover the casserole for the last 10 minutes of baking.