If you are going asian (an assumption on carmelized and pickled onions) you might want to try a rice vinegar, mirin and dried red chile sauce reduction. Like the viinegar sauce used in carolina boston butt recipes. Otherwise I would use one of the traditional BBQ sauces on this site (provided by some of the best BBQ people on the web) and cut it with a rich au jus to make a really nice dipping sauce. BOLHTH.
"In those days spirits were brave, the stakes were high, men were real men, women were real women, and small furry creatures from Alpha Centauri were real small furry creatures from Alpha Centauri. "
I would turn it into a banh mi style sandwich. Use a mix of mayo sriacha/sambal and top it with pickled julienne carrots and daikon radish. Then top that with fresh cilantro, green onion, and paper thin slices of red jalepeno.