Heat oven to 200C/180C fan/gas 6. Toss the chicken in the oil and 1 tsp of the curry powder, season and mix well to coat. Put the chicken on a foil-lined baking tray and bake for 20 mins until cooked through. Leave to cool a little, then slice.
Meanwhile, make the dressing. In a bowl, combine the remaining curry powder with the yogurt, chutney and lime zest and juice (add 1 tbsp water if the dressing is a little thick).
To serve, arrange the lettuce leaves on 2 plates. Top with the mango and cooked chicken, then drizzle with the dressing. Scatter with the red onion and sesame seeds before serving.