HEAT grill to medium-high heat.
RESERVE 1/3 cup dressing. Brush remaining dressing onto steak and cut sides of peppers.
PLACE steak and peppers, dressing-sides down, on grill grate. Grill 10 min. or until steak is medium doneness (160°F), turning steak after 5 min. (No need turn peppers.) Meanwhile, cover 4 serving plates with greens; top with tomatoes and onions.
CUT steak across the grain into thin slices; cut peppers into strips. Arrange meat and peppers over salads. Drizzle with reserved dressing.