1Mix vinegar, oil, sugar and salt. Reserve 1/4 cup for corn salsa.
2Spray broiler pan with cooking spray. Place mushrooms, stem sides up, in pan. Brush lightly with vinegar mixture. Broil about 6 inches from heat 2 minutes. Turn mushrooms; brush with remaining vinegar mixture. Broil 2 to 3 minutes longer or until tender. Remove from pan; cool 5 minutes.
3Mix corn, tomatoes, olives, parsley and reserved vinegar mixture. Cut mushrooms into 1/2-inch slices. Serve with corn salsa.