In a large bowl or plastic bag, combine chicken fillet, zucchini, onion, oil, oregano, 2 tbsp vinegar, 1/2 teaspoon. salt and 1/4 teaspoon. pepper. Leave to marinate at room temperature for 30 minutes.
Preheat the grill. Grease the wire rack with oil. On each wooden skewer, string 3 cubes of zucchini, chicken fillet and onion. Fry for 12-14 minutes.
Prepare the sauce. In a blender, combine the cheese, yoghurt, mint and remaining vinegar. Serve kebabs with sauce, garnish with mint leaves. Serve boiled rice as a side dish for kebabs (optional).