Add the vegetable stock to a large saucepan and bring to a boil. Reduce to a simmer and add the lentils, cook for 25-30 minutes until the lentils are soft.

While the lentils are cooking, mix together the red wine vinegar, olive oil, lemon juice and mustard to make the dressing. Add the finely chopped parsley. Taste and season as you like. Pour the dressing into a large bowl

Core and finely slice the apple. Add to the bowl with the dressing and toss to coat it. This will prevent the apple going brown.

Toast the pine nuts in a dry frying pan for a few minutes until lightly golden. Set aside.

Drain the lentils and add to the bowl with the apple and dressing, toss until all is coated. Add a few handfuls of watercress and the pine nits and serve.