1 red onion, cut into 1/2-inch-thick rings (I cut them even thicker - think 1 inch so that they cook rather than burn or fall through the grates)
4 tablespoons extra-virgin olive oil
1/2 cup flat-leaf parsley leaves (this I skip if I don't have it on hand)
1 tablespoon balsamic vinegar (use as much as you think you need - probably more than this).
kosher salt and pepper
Add the parsley, vinegar, the remaining 2 tablespoons of oil, 1 1/4 teaspoons salt, and 1/4 teaspoon pepper to the potatoes and onion and toss to coat. Taste and see if you need more of anything. Serve warm or at room temperature.