2 x 125 g (4 oz) cans mackerel in oil or brine, drained and flaked
200 g (7 oz) firm goats' cheese, crumbled or diced
chopped chives, to garnish (optional)
Cook the dried lentils a large pan of lightly salted boiling water for 15–18 minutes until tender but still holding their shape. Drain and set aside.
Meanwhile, heat the oil in a large frying pan and cook the onion very gently for 12–15 minutes until really soft and golden. Pour the balsamic vinegar over the onion and simmer gently for 2–3 minutes until the vinegar begins to turn slightly syrupy.
Remove from the heat and gently stir the lentils into the onion with the beetroot. Set aside to cool slightly for 4–5 minutes, then spoon into dishes and scatter over the flaked mackerel and crumbled goats' cheese. Garnish with chopped chives, if desired, to serve.