Remove the skin from the salmon and cut it into chunks. Pulse in a food processor 5 or 6 times, or chop finely with a knife, until it holds together but is not a paste.
Mix with the egg, Dijon, sliced green onion, lemon juice and salt. Shape into 4 patties about 2 cm (3/4 inch) thick and chill for 10 minutes so they hold.
Heat the oil in a large non-stick skillet over medium heat until shimmering.
Cook the burgers for about 4 minutes per side, until golden and 63°C (145°F) in the centre.
Toss the coleslaw mix with the Greek yogurt, chopped dill and apple cider vinegar.
Toast the buns and serve the burgers topped with the dill slaw.