Wash the zucchini and peel them. If they're organic, grate them along with the rind. To drain them from the water easier, do the following.
Be sure to work on a cotton towel. Grate zucchini directly on top of it. Then fold the edges, drain out the water released by the veggies. Towels do an amazing job of absorbing the moisture and it's faster.
Unroll the towel and pour the grated zucchini in a bowl.
Add the grated feta cheese and cheese, finely grated dill, spices and the breadcrumbs. Separate the egg whites from the yolks. Add the yolks to the mixture, beat the egg whites to snow in a separate container.
Mix together all of the components and shape meatballs. The texture must not be sticky to the fingers, so if necessary, add more breadcrumbs. The drier the mixture is, the less oil the meatballs will absorb during frying.
Prepare 3 plates: 1 with breadcrumbs, 1 with the whites for dipping the meatballs, and another laid out with paper towels.
Roll the zucchini meatballs in breadcrumbs, then in the beaten whites and in the breadcrumbs again.
Fry in heated oil on both sides until they obtain a light golden crisp but be careful not to over-fry them.
For the yoghurt sauce, lightly heat up fennel seeds, as these will boost the flavor. While still hot, put them in a mortal and pestle and grind finely. Add salt and the garlic cloves. Add the strained yoghurt and finely chopped dill.
You can serve the zucchini meatballs hot or as a cold appetizer, garnished with the yoghurt sauce.