Heat the oil in a saucepan, add the onion and fry for 2—3 minutes until it is beginning to soften.
Add the lentils and stock, bring to the boil, then cover and simmer for 30—40 minutes until the lentils are tender and the stock has been absorbed. Add the tomatoes and spring onions to the lentils. Stir well to mix.
Meanwhile, make the salsa by putting the herbs, capers, anchovies (if used), oil and lime rind and juice in a food processor and whizzing for a few seconds until combined but still retaining a little texture.
Drizzle the salsa over the warm lentils and toss together. Serve with toasted chapattis or flat breads.