Heat oil in a pot and saute the chopped onion at moderate temperature. Gradually, add the chopped carrot and red pepper. Cook with the lid closed until all ingredients soften well.
Next, add the chopped potatoes to them, as well as the chopped celery. Stir and add about 8 1/3 cups (2 L) water. Let the mixture come to a boil, while you get to work on the mince in the meantime.
Season it with the spices and half the parsley and knead. Put it in the fridge to firm up a bit. Once the soup begins to boil, form meatballs and add them in. When they float up to the surface, it means they're boiled. Add the vermicelli. Season to taste and leave the soup to simmer on low heat about 15 min.
In the meantime, prepare the thickening agent. Beat the yoghurt and eggs. Scoop a little of the soup with a ladle and once it cools a bit, pour it to the egg mixture in a thin trickle, stirring vigorously.