In large skillet, heat 1 tablespoon of the oil over medium-high heat. Sprinkle steaks with 3/4 teaspoon of the pepper and the salt. Add steaks to skillet; cook 6 to 8 minutes, turning once, until of desired doneness. Remove steaks to plate; cover to keep warm.
In same skillet, heat remaining 1 tablespoon oil over medium-high heat. Cook onion in oil 4 minutes, stirring frequently, until tender. Stir in vinegar and remaining 1/4 teaspoon pepper; cook 3 minutes or until liquid is reduced to 1/2 cup.
Spoon 2 tablespoons balsamic onion mixture over each steak; sprinkle each with 2 tablespoons cheese.