Preheat oven to 400F. First make pesto. Spread the pistachios out on a large baking tray. Bake in the oven for 4-5 minutes until toasted. Leave to cool.
Add the cooled nuts to a food-processor along with the garlic. Roughly chop the avocado flesh. Add this to the food-processor, along with the lemon juice, grated cheese and mint leaves and 2 tablespoons of cold water.
Add a good pinch of salt and pepper. Pulse to make a chunky, pesto-like consistency - add a little more water, if needed, or lemon juice to taste.
Next cook the pasta in boiling, salted water until al dente. Add the peas to the pan for the last minute of cooking time.
Drain well, reserving a couple of tablespoons of the cooking water and return to the pan. Add the grated zucchini and pesto, along with the reserved water to loosen. Toss together. Serve with grated cheese and mint leaves.