Simmer the green or puy lentils in unsalted water for 20-25 minutes until tender but still holding shape. Salting the water early keeps their skins tough.

Whisk the lemon juice, mustard, olive oil, salt and pepper into a dressing.

Drain the lentils and, while still warm, toss them through the dressing. Leave 10 minutes.

Soak the thinly sliced red onion in cold water for 5 minutes to take the harsh edge off, then drain.

Fold in the halved tomatoes, diced cucumber, onion and chopped parsley.

Crumble the feta over at the end rather than mixing it through, so it stays in distinct pieces.