Put the petit pois in a pan of cold water, bring to the boil and cook for 2 minutes, until just tender. Drain and set aside.
Place the spinach in a colander over the sink and pour a kettle full of boiling water over the leaves until they are wilted. Run under cold water to cool, then squeeze out all the excess water.
Put the spinach in a food processor with the petit pois, avocado, soft cheese and mint, and whizz until smooth. Season to taste and spoon into a serving bowl.
Use a bat-shaped (or another spooky shape) cutter to cut out shapes from the cheese slices, then serve with the vegetables alongside the dip.