Melt Promise® Buttery Spread in 12-inch nonstick skillet over medium-high heat and cook mushrooms, green beans and onion, stirring occasionally, 6 minutes or just until tender. Season, if desired, with freshly ground black pepper. Cover and let steam 3 minutes.
Meanwhile, evenly arrange salad greens on two dinner plates. Evenly top with warm vegetable mixture and juices, tuna and tomatoes. Drizzle with vinegar and garnish with cheese.