Grilled onions

I've been experimenting with grilled onions a bit lately.  I slice them about 1/4 inch thick, put at least two toothpicks in them (so they don't fall apart on the grill - much better than a grill basket), and then add olive oil, balsamic, fresh herbs, and some kosher salt.  Below is a red onion with rosemary, but a yellow onion with thyme is my current favorite.  Let the onions sit in the oil and vinegar for about 20-30 minutes so the liquid can get inside the rings, then grill it up to your preferred blackness.  It's a delicious contorno - enjoy.