Place the chillies, lemongrass paste, fish sauce, sugar, salt, cumin, spring onions, kaffir lime leaves, garlic and ginger into a food processor. Pulse until well chopped. Add the salmon fillets and coriander then pulse a few times until the salmon breaks down and everything is combined.
Shape the mixture into four balls using your hands. Place them on a plate and heat up the griddle.
Brush half the oil on the salmon burgers and the rest of the oil on the griddle. Place the burgers on the griddle and flatten slightly with a spatula. Cook for 2-3 minutes until griddle lines appear, then turn over and cook again for a further 2-3 minutes until cooked in the middle (you can open one up to check).
Place the buns on plates. Top with the salad leaves and strips of carrot. Add the burgers, cucumber strips and onion slices, then drizzle on the chilli sauce before putting the top of the bun on the burger.