Put the onion, curry paste, sesame oil, soy sauce and most of the coriander into a food processor. Reserve a third each of the prawns and squid, then add the rest to the processor. Whiz to make a smooth paste, then add remaining prawns and squid and pulse until the mixture is chunky. Form into large patties with the aid of the flour. Heat a pan with a little oil and cook the patties on one side. Brush the top with a little oil and flip over to continue cooking on the opposite side. Meanwhile, mix together the mayonnaise and the sweet chilli sauce. Cut the buns in half and lightly toast them. Spread half of the chilli mayonnaise on to the base of the bun. Lay over some mixed salad leaves and pop the burgers on top. Peel, stone and slice the avocado and place the slices on top of the burgers. Spoon over the remaining chilli mayo and serve with the bun lids on the side.