Heat the carrot juice and add the gellan, bring to the boil, whisking to incorporate the gellan. Pour into a mould and leave to set.
Melt the Parmesan cheese in a hot non-stick frying pan, remove and cut into strips. Leave to cool until they are crispy.
Salt the mackerel fillets, leave for 10 minutes then rinse and dry.
Heat the white wine vinegar, add the spices and sugar, bring to the boil then leave to cool. Strain and pour into a plastic container. Add the mackerel fillets and leave to pickle for 20 minutes.
Bring the beetroot juice to the boil, season with salt then add the gellan. Pour into moulds and leave to set.
Serve with thinly sliced goat’s cheese and watercress.