For the dressing: Add the peanut butter, oil, yogurt and all but a splash of the lemon juice and mix until well combined. Season with salt and pepper and loosen with a little extra olive oil if needed.
For the salad: Discard any damaged outer leaves of the lettuce and then cut into wedges lengthways, either quarters or sixths if slightly larger than usual.
Using a sharp knife cut the apple into quarters and discard the core. Carefully cut the apple into thin matchsticks and place in a bowl. Add the reserved splash of lemon juice from the dressing to stop the apple from browning.
Using a Y-peeler, peel the carrots and cucumber into ribbons and place in the bowl with the apple. Thinly slice the radishes into rounds or half-moons, depending on size, and add to the bowl.
To serve, generously spread some of the dressing on the bottom of a long serving plate. Arrange the lettuce wedges over the top. Layer around and on top of the lettuce the apples, radishes and carrot and cucumber ribbons. Garnish with the pistachios and pomegranate seeds. Serve with additional dressing on the side.
If you have a mini food processor, use that for the dressing. Alternatively, this is a great way to use up the last bit of peanut butter in a jar; just add the remaining ingredients and shake!