Mackerel with Puy lentils and parsley - River Cottage

Ingredients

• 150–250g cooked mackerel, broken into flakes
• 1 small red onion, or ½ large one, halved and finely sliced
• 150–200g cooked Puy lentils
• 2 tablespoons roughly chopped flat-leaf parsley, plus extra to finish
• Sprig of dill or tarragon, chopped, or a few basil leaves, roughly shredded (optional)
• Salt and freshly ground black pepper
• 2 tablespoons rapeseed or olive oil
• 1 tablespoon cider vinegar or lemon juice
• ½ teaspoon mustard
• Lemon wedges