Meanwhile, crumble sausage into large skillet sprayed with cooking spray. Add onions; cook on medium heat 8 min., stirring frequently. Stir in peppers; cook 4 to 6 min. or until sausage is evenly browned, stirring frequently. Add dressing; mix well. Simmer on medium-low heat 8 to 10 min. or until peppers are crisp-tender.