What would be a non-pork alternative to the pork belly? Would chicken work?

Jajangmyeon is also made using ground meat and seafood- just as authentic and equally as good. You could use ground beef or chicken, or even shrimp. The main flavor is the black bean sauce anyway, and the Koreans and Chinese both use other meats all the time. One of the best versions I had was made with leftover beef flanken cut ribs, bone bits removed and cut into bits.

Maybe dice up duck breast (including the skin)? I know people make duck "bacon" so maybe that would work?