Creamy Chicken and Mushroom Casserole

Preheat the oven to 325 degrees F (165 degrees C).

Bring a large pot of lightly salted water to a boil; cook rotini at a boil until tender yet firm to the bite, about 8 minutes. Drain, reserving 1/2 cup cooking liquid for the sauce.

Heat olive oil in a large frying pan or Dutch oven over medium heat. Gently saute celery, onion, and bell pepper until onion is translucent, 5 to 7 minutes. Add the mushrooms and toss. Sprinkle vegetable mixture with flour; stir until flour begins to congeal and cook. Stir in chicken broth until it begins to thicken. Reduce heat to low, cover, and cook for 10 minutes. Stir in mushroom soup, reserved pasta cooking liquid, chicken, and peas until blended.

Mix pasta and sauce together in a 2-quart casserole dish. Top with Parmesan cheese. Cover.

Bake in the preheated oven for 20 minutes. Uncover and continue to bake for another 5 minutes.