2) Cut rolls in half most of the way through, then carefully remove a strip of bread from inside of each half roll. Set rolls aside.
3) Place bread strips in food processor, cover and process to make make crumbs.
4) Combine breadcrumbs, minced beef, yogurt, oregano, salt and 1/2 teaspoon pepper in large bowl and mix lightly but thoroughly.
5) Divide beef mixture into 16 equal portions and shape into meatballs, then place on rack in a roasting pan.
6) Bake in preheated oven for about 18-20 minutes until there is no pink in the centre and the juices run clear.
7) Meanwhile, combine all of the yoghurt sauce ingredients in a small bowl and set aside.
8) Place four meatballs in each roll, top with creamy yoghurt sauce and garnish with slices of tomato, cucumber and olives, as desired
Cook's tip: for six servings, remove strip of bread from six rolls as directed above. Shape beef mixture into 18 meatballs. Bake as above, place threee meatballs in each roll and top as required.