Cover bottom of skillet with approximately 1/2 inch of cooking oil and bring to a medium-high heat. Drop in potato strips and fry until golden brown; remove, drain, and set aside. Pour off all of oil xcept 3-4 tb.

Stir the cornstarch into the water and add the fish sauce. Reheat the remaining oil in skillet and briefely sautee the onion wedges and garlic. Next add the beef and stir-fry for approximately two minutes. Then add the tomato cubes and the green onions. As you stir, add the cornstarch mixture. Cook for 3-4 minutes, until the liquid is reduced slightly.

Return the potatoes to the skillet. Strir well and allow time just to heat through. Add pepper to taste. Serve.