The red onions on the pizza are dynamite BUT what might also be nice, whuch i a pleasant addition to any pizza, a cold pickly salad garnish. I suppose even cole slaw would be nice but thats a little too normal. You dont want your bbq pizza to taste too much like a pulled pork sandwich.
So my suggestion is to garnish your cooked pizza with a relish of bread and butter pickles and pickled jalapenos tossed with thin sliced raw onion. Now mind you, ive never made any such animal so dont pay me no mind. Pizza looks awesome.