In 12-inch nonstick skillet, melt 4 tablespoons Country Crock® Spread over medium-high heat and cook mushrooms and onion, stirring occasionally, 2 minutes or until starting to brown. Reduce heat to medium and cook, stirring occasionally, 6 minutes or until tender and dark golden brown. Stir in 1/2 teaspoon salt and 1/4 teaspoon pepper. Remove vegetables; keep warm.
Season steaks with remaining 1/2 teaspoon salt and 1/4 teaspoon pepper. In same skillet, melt remaining 2 tablespoons Spread over medium-high heat and cook steaks, stirring occasionally, 2 minutes or until desired doneness. Remove from heat, then top steaks with cheese. Cover 1 minute or until cheese is melted.
On rolls, arrange steak. Drizzle, if desired, with pan juices. Evenly top with vegetable mixture.