Preheat the oven to 200°C.
Cut the bacon into thin strips. Slice the leek and drain the lentils.
In a heavy-based, oven-proof dish, heat the oil, brown the chicken legs on each side, then transfer them to a plate.
Add the bacon, fry until crispy, then add the leek and garlic.
Put 4-5 sprig of thyme aside, add the leaves of the rest to the he pan. Stir for 2 minutes, then pour in the stock. Return the chicken to the dish.
Add the lentils and tomatoes. Gently stir, then place the chicken legs on top of the vegetables. Put the thyme on top and season to taste.
Put the dish in the oven and bake for about 15-20 minutes.
Serve warm with bread, mashed potatoes or rice.