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.