Or you can make the soup in the crockpot, and do the dumplings separately on the stove: Pour about an inch of chicken broth into a shallowpan and bring to a boil.
Serve out a portion of the udon in a warmed shallow bowl or small cast iron pan, place clams and prawns on top, ladle hot broth over the top, sprinkle with coriander and finish with a couple of lime wedges.