Heat Oil In A Large Skillet Over Medium High Heat. Saute Onions And Potatoes Until Slightly Browned, Then Stir In Corned Beef. Season With Pepper And Add Vinegar 1 Tablespoon At A Time, Cooking For 3 To 5 Minutes In Between Each Addition. Partially Cover Skillet, Reduce Heat To Medium-Low And Cook, Stirring Occasionally, For About 20 Minutes Or Until Potatoes Are Tender.