Using a large mortar and pestle, pound the lemongrass, shallot and chilli to a rough paste. Add the pork, sugar and a pinch of sea salt and pound again. Add the spring onion, dill and lime leaves and pound well. Add the fish sauce and half the padek or mam nem and pound again. Working from the top of each capsicum, slice down one side down to the stem, using a sharp knife. Remove the seeds by scraping them out with a small spoon, then discard. Stuff the capsicums with the pork mixture and set aside.
Heat a barbecue chargrill or chargrill pan to medium-high. Place the banana leaves on top of the grill to stop the capsicums burning. Chargrill the capsicums on top of the banana leaves for 7-8 minutes each side, basting them with the remaining padek or mam nem as they cook.
Serve hot, with sticky rice.