This relish for grilled and barbecued foods lies somewhere between a salad and a sauce. Roasting the onions before combining with seasonings intensifies the flavor and sugar mellows any harshness.
Set onions in pan in preheated 375-degree oven and roast until not quite tender throughout—about 35 minutes; they should still be slightly crisp-firm in the center.
Let stand until cool enough to handle. Peel, then cut