1Set oven control to broil. Spray broiler pan rack with cooking spray. Brush dressing on both sides of mushrooms; reserve remaining dressing. Place mushrooms on rack in broiler pan. Broil with tops 2 to 4 inches from heat 4 minutes; turn. Broil about 3 minutes longer or just until mushrooms are tender.
2Meanwhile, divide salad greens among 4 plates. In small bowl, mix cheeses; spread on toast.
3Place mushrooms on salad greens. Top with tomatoes. Drizzle with remaining dressing. Serve with toast.