Put the potatoes in a pan, cover with cold water and bring to the boil. Cook for 15 minutes until tender. Drain and set aside.
In a small bowl, mash the goat's cheese with the olive oil. Roll spoonfuls of the mixture into 8 balls. Chill in the fridge for 10 minutes. On a small plate, mix the pistachios and half the parsley together and roll the balls in the mixture. Sprinkle with cayenne pepper.
Meanwhile, put the beans in a pan of boiling water and simmer for 2-3 minutes. Drain and refresh in cold water, then set aside.
Put the cooked Jersey Royals and green beans in a large bowl and gently toss with the goat's cheese balls, radishes, tomatoes, onion, cucumber, salad and the rest of the parsley. Serve with a drizzle of French dressing.