Place all of the pesto ingredients in a blender or food processor and whiz up until you have a green, bubbly sauce, adding a splash of water if the pesto is a little thick. Taste, season, and adjust anything that needs adjusting.

In a large saucepan, heat the olive oil and soften the onion. Add the zucchini, then pour in the stock and simmer on low for 8 to 10 minutes. Add the peas and arugula, bring back to a boil, and cook for another 3 or 4 minutes until the vegetables are tender.

Let the soup cool for 15 minutes or so and then, in careful batches, mix in a blender until you have a velvety purée. Reheat in the saucepan or serve cold, as it works either way. You can either run 4 tablespoons of pesto through the soup when you’re serving or reheating, if you are. Or, if serving cold, add it to the blender when you are puréeing the batches.