HEAT oven to 350ºF.
HEAT oil in large skillet on high heat. Add mushrooms and chopped onions; cook and stir on medium heat 3 min. or until onions are crisp-tender. Stir in beans; cover. Cook on medium-low heat 4 min. Remove from heat.
MIX next 4 ingredients. Add to vegetable mixture; mix well. Pour into 2-qt. casserole sprayed with cooking spray.
BAKE 40 min. or until heated through, topping with French fried onions after 30 min.