Wipe roast well and trim off excess fat. Lightly rub top of meat with oil. Dust with salt, peper and ginger. Insert cloves in roast. Place apples and onions in crockpot and top with roast (cut roast in half, if necessary, to fit easily). Pour in apple juice. Cover and cook on Low for 10 to 12 hours or on High for 5 to 6 hours.
Remove roast and apples to warm platter. Turn crockpot to High setting. Make a smooth paste of the flour and water; stir into crockpot. Cover and cook until thickened.
Serves 6 to 8.