1Peel potatoes; cut into 2x1/4-inch sticks. In 12-inch skillet, heat 1 tablespoon oil over medium-high heat. Cook potatoes in oil 5 to 8 minutes, tossing frequently, until tender and golden brown. Remove from skillet; keep warm.
2In same skillet, heat about 1 teaspoon oil over medium-high heat. Working in small batches, cook beef in oil about 1 minute or just until cooked. Continue cooking beef in small batches, using 1 teaspoon oil per batch. Remove beef from skillet; keep warm.
3Add red onion to skillet; cook and stir about 2 minutes or until tender. Stir in beef, tomatoes, soy sauce, vinegar and salt and pepper. Cook and toss mixture over medium heat about 1 minute or until hot.
4Spoon beef mixture onto large serving platter; top with cooked potatoes. Garnish with green onions. Serve over rice.