Preheat grill or grill pan to medium high heat (375 to 450 degrees F on a grill).
Peel and slice the onions into thin rounds.
Brush both sides of the onions with olive oil and sprinkle the salt, garlic powder, and pepper on them.
Place the onions on the grill and cook for 4 to 6 minutes on each side or until grill lines have formed and onoins are tender.
Remove the onions from the heat and allow to cool for a few minutes before serving.