1. Combine 1⁄4 cup of the yoghurt, the garlic, cumin, coriander, pepper, lime zest and 1⁄8 teaspoon of the salt in a large (3.5 litre) snap-lock bag. Massage the bag to mix the ingredients. Add the chicken and massage the bag to evenly coat the chicken. Press out all the air and seal the bag. Refrigerate for at least 2 hours or as long as 8, turning the bag occasionally.
2. Combine the remaining yoghurt, milk powder, ground flaxseed and remaining salt in another container. Stir until smooth. Add the cucumber, spring onion and mint (if using). Stir. Cover securely and refrigerate for up to 8 hours.
3. Preheat a barbecue or chargrill pan. Remove the chicken from the refrigerator 30 minutes before grilling. Brush the grill with a little oil and wipe off excess. Place the chicken on the barbecue or chargrill pan and cook for about 4 minutes on each side, or until a thermometer inserted in the thickest portion registers 70°C and the juices run clear. Remove the chicken and allow it to sit for 5 minutes before slicing it. Serve accompanied with the cucumber-yoghurt sauce and lime wedges.
Per serving: 785 kJ, 24 g protein, 8 g carbohydrates, 6 g fat (2 g sat fat), 61 mg cholesterol, 279 mg sodium, 1 g fibre, 214 mg calcium