Preheat oven to 425 degrees. Place ribs in a single layer in large roasting pan. Cover the ribs with chopped onion. Cover the pan with a double layer of heavy duty aluminum foil. Seal the foil tightly, very tightly, to make sure the steam stays inside the pan. Bake for 1 1/2 hours. Remove the pan from the oven and carefully remove the foil. Put the ribs in a large pan or bowl and cover with BBQ sauce. Let stand 30 minutes. On pre-heated grill barbeque the ribs for approximately 5-7 minutes.