Broil, 4 to 5 inches from heat source, 8 to 10 min. on each side or to medium doneness (160ºF). Meanwhile, heat dressing in large skillet on medium-high heat. Add onions; cook and stir 3 min. Add bell peppers and garlic; cook 5 to 6 min. or until vegetables are crisp-tender, stirring occasionally. Add tomatoes; stir. Cook 2 to 3 min. or until heated through, stirring occasionally.