Heat the oil in a skillet over medium low heat. Saute the onions until soft, about 5 to 7 minutes. Add the ginger and cook for 1 minute to release the aromas. Add the vinegar and simmer to reduce by half. Add barbecue sauce, brown sugar and pepper and simmer, stirring occasionally, until sauce thickens, about 15 minutes. Place the sauce in a blender and puree.

Heat a grill. Brush swordfish steaks with olive oil and sprinkle with salt and pepper. Grill fish about 7 minutes, brushing with ginger barbecue sauce. Turn, brush with barbecue sauce and grill another 3 minutes, or until cooked through.