To make the dressing, dissolve the sugar in 50ml water over a low heat. Bring to the boil and simmer until thick bubbles form. Take off the heat and pour in the chilli sauce and lime juice. Strain and cool. This will keep for a week in the fridge but must be brought back to room temperature before use.
For the salsa, mix all the ingredients in a bowl and season. Drizzle in enough oil to lightly coat. Store in an airtight container and chill (it will keep for 2-3 days in the fridge).
Toss the tofu in the flour, dusting off any excess. Heat a little oil in a shallow pan, add the tofu and fry for 2 minutes. Carefully turn and fry for 2 more minutes. Remove with a slotted spoon, drain on kitchen paper and sprinkle with salt.
To serve, pour the dressing into a sauce bottle with a thin nozzle. Zigzag the dressing onto the plate (if you don't have a sauce bottle you can use a spoon). Toss the watercress with the rest of the salad ingredients and throw in the tofu. Spoon some avocado into the centre of the plate and slightly flatten to resemble a thick disc. Pile the salad on top.