1Heat oven to 350°. Grease rectangular baking dish, 13x9x2 inches. Cook manicotti shells as directed on package.
2Melt margarine in 10-inch skillet over medium-high heat. Cook bell peppers and onions in margarine 2 minutes; stir in mushrooms. Cook 2 to 3 minutes longer or until peppers are crisp-tender. Stir in sun-dried tomatoes, vinegar and cheese.
3Fill shells with mushroom mixture. Place in baking dish. Mix Alfredo sauce and 2 tablespoons water. Pour sauce over shells. Cover and bake 30 to 35 minutes or until hot and bubbly.