Preheat oven to 350°.
Heat oil in a large nonstick skillet over medium-high heat. Add mushrooms; sauté 5 minutes or until tender. Combine mushrooms and remaining ingredients except cooking spray in a large bowl, stirring until well blended.
Spoon mixture into a 2-quart casserole coated with cooking spray. Bake at 350° for 30 minutes or until thoroughly heated.