Heat oil in a large pot and cook onion, carrots and celery for 6 minutes. Add garlic, cumin and coriander and stir for 30 seconds.
Add lentils, broth and bay leaf. Bring to a gentle simmer and cook for 15 minutes.
Stir in chicken, salt and pepper and simmer partly covered for 20 to 25 minutes more until the lentils are tender and the chicken reaches 165°F.
Remove the bay leaf and stir in lemon juice off the heat.
Let stand for 5 minutes, stir from the bottom and serve with the lentils and chicken evenly distributed.