Heat oven to 350°F. Spray 13x9-inch (3-quart) glass baking dish with cooking spray. Cook pasta as directed on package, adding frozen peas during last 3 minutes of cooking time; drain and return to saucepan.
Meanwhile, in 12-inch skillet, cook bacon until crisp; drain on paper towels. Reserve drippings. Crumble bacon; set aside. Cook onion and mushrooms in bacon drippings over medium heat 5 minutes, stirring occasionally, until tender.
In large bowl, mix the pasta and peas, mushroom mixture, chicken, Alfredo sauce and 1/2 cup of the cheese until blended. Spread in baking dish. Sprinkle with bacon and remaining 1/2 cup cheese.
Bake uncovered 20 minutes or until cheese is melted.