Put the vinegar, sugar, 100ml of water and a little seasoning into a small pan and heat until the sugar dissolves.
Use a mandoline or sharp knife to cut very thin slices of beetroot, then put into a bowl and pour over the hot pickling liquid. Cool to room temperature, then chill for 2 hours.
Put the goat’s cheese into a bowl and use a wooden spoon to beat until smooth. Stir in the lemon zest and juice, parsley, salt and plenty of pepper.
Drain the beetroot slices really well and pat dry with kitchen paper. Spoon or pipe a little of the filling onto one half of each beetroot slice, add a little walnut, then fold over gently. Repeat with the remaining slices and filling.