Lentil soup with leftover lamb

I overestimated our guests' ability to eat lamb meat, so today I made lentil stew with lamb roast leftovers (300 g, chopped in small cubes).  You need to prepare soffritto/mirepoix of finely chopped (use food processor) one large carrot, two stalks of celery and one large onion. Pour in a pot 4 tbsp of extra virgin olive oil and start cooking the flavour base. As the onion becomes translucent, pour in beluga lentils (1,5 dl), red (1 dl) and green (1,5 dl) lentils and keep cooking until the lentils are coated with flavour base. Now add enough vegetable stock to cover the lentils and the meat, and let simmer until lentils are soft. Serve with stale bread and sprinkle of chives. 

Three types of lentils in this recipe; Beluga, red and green ones. As a thumb rule for every one decilitre of dry lentils, you need two decilitres of water.