Bing? Ding? Wikipedia's compilation of cross-linguistic cognates of onomatopoetic sounds includes listings for dogs and cats, clocks and cannons, sneezing and laughing, but there's no mention of the ting-a-ling that signals the end of the toasting cycle.
Thinking back on a griddled chive flatbread procured in a Shanghai alley, I sent my green onion bings (bag of five; 450 g.; $2.99) to the frying pan (and so have no new evidence, but I'd say "ding"; how about you?). The flatbreads offered little green onion flavor, and I doubt that the other varieties, yam paste and "red filling," would make a better account. The supermarket itself, though not brimming with exotica, is large, bright, well-stocked, worth a look-see.
Great Wall Supermarket
137-45 Northern Blvd. (Linden Pl.-Leavitt St.), Flushing, Queens
718-353-9828
(One of many locations)
www.GW-Supermarket.com