1. Heat a drizzle of oil in a large pot on medium to high heat. Add bacon and cook for about 2 minutes. Reduce heat to medium and add onion, carrots, celery and leek. Stir, cover and cook for 4-5 minutes, stirring occasionally until vegetables are just tender.
2. Pat chicken dry with paper towels and season with salt. Add to pot with thyme, lentils, stock, water and salt and bring to a simmer while stirring. Reduce heat to low, cover and simmer gently for 15-20 minutes until chicken is cooked and lentils are tender.
3. Using a slotted spoon, remove chicken from soup and roughly dice or shred and return to pot. Stir in sour cream and season to taste with salt and pepper.