For the lentil stew, soak the lentils overnight in 1/2 l water.
Drain the lean yogurt in a coffee filter.
Boil potatoes in their skins and then peel them.
Cut onion into rings, sauté briefly in oil until translucent.
Add lentils with soaking water, vegetable soup seasoning and bay leaf, cook for about 20 minutes.
Slice carrots and dice celery, add after 10 minutes of cooking.
Serve stew in deep plates with potatoes, sprinkled with a blob of lean yogurt and chopped parsley.