Place the garlic, ginger, soy sauce and sunflower oil in a bowl and whisk together. Add the chicken breasts and turn to coat both sides, then leave to marinate for 15 minutes.
Place the potatoes in a saucepan, pour over boiling water to cover and add the mint sprigs. Cook for 15–20 minutes or until tender. Meanwhile, place the asparagus in a steamer basket or metal colander, cover and set over the pan of potatoes to steam. Cook thin spears for 4–5 minutes and thick spears for 8–10 minutes, or until just tender. Drain the potatoes (discard mint) and leave until cool enough to handle, then cut into thick slices. Cut the asparagus diagonally into 6 cm lengths.
Preheat the grill to medium. Remove the chicken from the marinade and place it on the grill rack. Grill for about 15 minutes, brushing frequently with the marinade and turning once, until cooked through and the juices run clear when the chicken is pierced with the tip of a knife. Leave to rest for 3–4 minutes, then slice.
To make the orange dressing, place the orange rind and juice, mustard, and sunflower and walnut oils in a large serving bowl, and whisk all the ingredients together until slightly thickened. Season with pepper.
Transfer the warm sliced chicken, potatoes and asparagus to the serving bowl and gently toss together to coat with the dressing. Add the mango and salad leaves and toss gently again. Serve immediately, while still warm.