Start by preparing the pesto; place the basil, rocket, extra-virgin olive oil, hazelnuts, garlic and a little salt in a food processor. Blitz until smooth. Add the Parmesan and pulse until a thick consistency is reached. Cover and chill until needed.
Make the gnocchi by boiling the potatoes whole and unpeeled in salted water until they are easily pierced by a fork.
Meanwhile, place the spinach in a steamer and steam over a saucepan of gently simmering water until wilted. Remove from the steamer and press through a sieve to get rid of any excess water. Roughly chop and set to one side.
Drain the potatoes and allow to cool until still slightly warm. Peel the skins and use an electric hand whisk to beat the potato flesh until smooth. Stir in the flour, chopped parsley, chopped spinach and 1 tsp of salt mixing well until combined. Knead this mixture on a lightly floured surface until no longer sticky. Add a little extra flour if needed during this stage so that you have a smooth dough. Take care not to overwork the dough – this stage should take no longer than 4-5 minutes.
Divide the dough into 4 and roll into long sausages roughly 3cm in diameter. Cut the sausages up horizontally into small chunks. Arrange on floured tray until ready to cook. When ready bring a large pan of salted water to the boil and cook the gnocchi for 4-5 minutes or until they rise to the surface.
Remove the pesto from the fridge and place in a large saucepan. Warm gently over a gentle heat; remove the gnocchi with a slotted spoon and toss in the pesto. Arrange on serving plates and garnish with the lemon zest and sprigs of parsley.