Heat the oil in a heavy based saucepan, add the chicken pieces and fry until slightly golden. Take the chicken out of the pan. Add the onion, garlic and celery and soften gently; this will take about 15 mins.
Add the carrots and parsnips (or sweet potatoes) and move around in the pan slightly until golden.
Return the chicken to the pan; add the lentils and water or stock and chopped herbs. Cover and simmer gently for 25 mins or until the chicken and lentils are cooked. Tear or cut the chicken into smaller pieces for toddlers and purée for babies.