Cook the potatoes in boiling, salted water for about 15 minutes until tender. Add the onion and red capsicum, return to simmering point and drain into a colander.
Meanwhile, use 1 tablespoon of the oil to brush the chicken thighs and sprinkle both sides with salt and pepper. Cook them in a pan, turning them once, until cooked through. Remove and set aside.
Put the honey, mustard, vinegar and remaining oil into a small screw-top jar with a pinch of salt and shake vigorously to emulsify. Put the drained, cooked vegetables into a wide dish, sprinkle with salt and pepper, then add the dressing and toss.
Scatter the salad leaves over the cooked vegetables and toss together gently. Cut each chicken thigh into 3 pieces, add to the salad, toss briefly and serve.