Chicken Shawarma with Garlic Sauce

• 500 g chicken thigh fillets
• 1 tbsp extra virgin olive oil
• 2 tsp cumin
• 2 tsp paprika
• 2 garlic cloves, crushed
• 1 small iceberg lettuce, shredded
• 1 Lebanese cucumber, sliced
• 2 tomatoes, diced
• 4 flat bread or wholemeal pita bread
• .5 cup Greek yoghurt
• 3 tbsp lemon juice