BROWN meat with onions in large skillet on medium heat. Stir in 1 cup tomato sauce, 1 cup water and dressing mix. Bring to boil. Stir in rice; cover. Remove from heat. Let stand 5 min.
MEANWHILE, heat oven to 400°F. Cut tops off peppers; discard seeds. Mix remaining tomato sauce and water in bottom of 9-inch baking dish. Add peppers; fill with meat mixture. Cover.
BAKE 35 to 40 min. or until peppers are tender. Spoon sauce from bottom of dish over peppers just before serving.