Place potatoes in a large pot filled with cold water. Bring to a boil, add salt and continue boiling over medium-high heat until potatoes are just tender. Drain.
In a large bowl, toss potatoes with onions, pepper and butter or olive oil. Pour in barbecue sauce and stir until potatoes are coated.
Transfer potatoes to a baking dish or aluminum foil pouch. Bake at 375 degrees for 20-25 minutes or grill in pouch for about 20 minutes.