In a large bowl, mix the mince, cumin and a little salt and pepper together well.
Divide the mixture into 16 even-sized pieces. Roll each piece into a ball about the size of a golf ball and set aside.
Heat a large frying pan, or two smaller frying pans, over a medium heat. Once hot, add a dash of oil and carefully put the meatballs in the pan. Cook for 15 minutes, or until cooked through, rolling the meatballs around from time to time to ensure even cooking on all sides.
Meanwhile, make the salad. Cut the tomatoes into cubes and put them in a bowl. Cut the cucumber into cubes and add to the salad bowl. Drizzle over a little oil and sprinkle with the mixed herbs. Season with a pinch of salt and pepper and toss together to make sure all the vegetables are evenly coated in oil and herbs. Set aside.
Mix together the yoghurt and mixed herbs and season to taste.
Lightly toast the pitta breads and cut open. Lay a few lettuce leaves inside each pitta. Top with four meatballs and spoon over the herby yoghurt. Serve immediately with the salad on the side.