Add chopped onions and jalapeños to a small mixing bow. Stir together the vinegar, brown sugar and salt until the sugar and salt have dissolved. Pour over the onion mixture and let soak for ½ hour. Drain and then stir in the bacon and mustard. The relish will keep covered in the refrigerator for up to 5 days.
Recipe by Grilling Outdoor Recipes powered by Bull Outdoor Products at https://blog.bullbbq.com/american-wagyu-burger-with-bacon-jalapeno-relish/