Chicken Tetrazzini

Preheat oven to 350 degrees F (175 degrees C).

Grease a 9x13-inch baking dish.

Bring a large pot of lightly salted water to a boil.

Cook spaghetti in the boiling water until cooked through but firm to the bite, about 12 minutes; drain.

Transfer to a large bowl.

Melt margarine in a skillet over medium heat.

Cook and stir onion in melted margarine until soft and translucent, 5 to 7 minutes; add to the spaghetti along with chicken, evaporated milk, cream of chicken soup, 4 ounces shredded Cheddar cheese, celery salt, salt, and black pepper.

Toss mixture to evenly mix; transfer to prepared dish.

Sprinkle 4 ounces shredded Cheddar cheese over spaghetti mixture.

Bake in preheated oven until cheese is melted and mixture is bubbling, about 45 minutes.