1. Place the chopped tomato, pepper, red onion and cucumber in a bowl then mix in the olives and spinach leaves.
2. Crumble the feta on top then drizzle with olive oil and season with salt and pepper.
3. Cook the burgers on an oven tray for 20 minutes at 180°C, turning once halfway through cooking.
4. Make the yoghurt dressing by mixing all the ingredients and seasoning with salt and pepper.
5. Warm up the pitta breads and fill each with lettuce, a cooked burger, the feta mix and top with a generous spoonful of yoghurt dressing.