1.In A Large Skillet, Brown Roast In Oil Over Medium-High Heat. Cut In Half; Place In A 5-Qt. Slow Cooker. Add The Onion, 1/2 Cup Teriyaki Sauce And Pineapple Juice. Cover And Cook On Low For 7-8 Hours Or Until Meat Is Tender. 2.Remove Roast; Set Aside. In A Small Bowl, Combine The Flour And Remaining Teriyaki Sauce Until Smooth; Stir Into Cooking Juices. Cover And Cook On High For 30-40 Minutes Or Until Thickened. Shred Meat With Two Forks; Return To The Slow Cooker And Heat Through. Spoon 1/2 Cup Onto Each Bun; Top With A Slice Of Pineapple.