For the sashimi, arrange the fish slices on a plate and cover with cling film. Place into the freezer to chill for 8-10 minutes, then remove and sprinkle over the salt and oil.
For the dressing, heat the oil in a pan and gently fry the onion, ginger and chilli for 2-3 minutes, or until softened. Stir in the Tabasco and soy sauce and cook for 3-4 minutes, or until the liquid has reduced by half.
To serve, spoon the dressing around the plate of sashimi and garnish with a sprig of fresh dill and the sliced chilli.