Place the chillies and salt in a medium sterilised jar and mix well. Seal the jar and store in the fridge for 3 days.
On the third day, drain the chillies, transfer them to a food processor and blitz: you can either blitz well to form a fine paste or roughly blitz so that some texture remains.
Add the vinegar and lemon juice, mix to combine, then return the mixture to the same jar. Pour enough olive oil on top to seal, and keep in the fridge.