Clean the leek, wash it and cut it into rings. Peel garlic and cut into thin slices. Wash the thyme, dab dry, put something aside for garnishing. Remove the remaining leaves.
Wash the chicken filet, dab dry and cut into strips. Heat oil in a pot, fry chicken meat in it, take it out. Sauté garlic and thyme in frying fat. Add lentils, deglaze with chicken stock and strained tomatoes.
Let everything simmer for about 15 minutes. Add leek and chicken meat about 8 minutes before the end of the cooking time. Season to taste with salt and pepper. Garnish with set aside thyme.