1Preheat oven to 350 degrees F (175 degrees C). Prepare a 13x9-inch baking dish with nonstick cooking spray.
2Bring a large pot of lightly salted water to a boil. Cook the rotini at a boil until tender yet firm to the bite, about 8 minutes; drain. Pour rotini into prepared baking dish.
3Melt butter in a heavy saucepan over medium heat. Cook and stir onions, celery, and bell pepper in melted butter until softened, about 5 minutes.
4Stir milk, cream of mushroom soup, poultry seasoning, salt, and black pepper into the onion mixture. Reduce heat to medium-low and bring to a simmer; about 5 minutes. Add chicken and 1/2 cup Cheddar cheese to the milk mixture; remove immediately from heat and pour over the rotini. Top pasta and sauce mixture with remaining Cheddar cheese.
5Bake in preheated oven until cheese is melted and beginning to brown, about 25 minutes.
Footnotes
Tip
Aluminum foil helps keep food moist, ensures it cooks evenly, keeps leftovers fresh, and makes clean-up easy.