In 10-inch skillet, heat oil over medium-high heat. Add beef. Cook, stirring frequently, about 3 minutes or until golden brown; reserve in medium bowl. In same skillet, cook onion about 3 minutes or until brown. Add tomato, beef, soy sauce, vinegar and pepper. Cook 2 to 3 minutes or until liquid has evaporated. Remove from heat. Cool 5 minutes.