Chicken tikka burgers

Name: Chicken tikka burgers
Prep time: 20 min
Cook time: 15 min
Total time: 35 min
Cuisine: Indian
Ingredients: 6 small chicken breasts; 6 burger buns (we used ciabatta); 2 tbsp tomato purée; 200g pot Greek yogurt; thumb-sized piece ginger , very finely grated; 4 garlic cloves , very finely grated or crushed; 2 tbsp garam masala; ½ tsp ground cinnamon; ½ tsp ground cayenne pepper; juice 1 lemon , plus wedges to serve; 2 tomatoes , chopped; 1 small red onion , chopped; 1 green chilli , chopped; 1 tsp tamarind pulp; 2 tbsp tomato ketchup; ½ cucumber , sliced; 1 Little Gem lettuce , shredded; small bunch mint , leaves picked; 1 small red onion , halved and finely sliced