Add walnuts, olive oil, garlic and a pinch of salt to a food processor and blitz until smooth. Take the herbs from the water and shake off any excess (but don’t fully dry). Add herbs to the food processor (tearing any big basil leaves) and blitz until evenly combined (about 5 to 6 pulses). Add the cheese, lemon zest and lemon juice and blitz until just combined (about 5 more pulses). If the pesto is too thick, pulse some of the cold soaking water (a few teaspoons at a time) until it’s a smooth, creamy texture. Season to taste with additional salt.