First make the dressing. Finely grate the zest of 1 orange into a bowl. Add its juice, the honey and lemon juice and 1 tablespoon olive oil. Peel 1/2 inch or so of ginger and chop it as finely as possible; then crush the small garlic clove. Add both these ingredients to the bowl with a little salt and pepper. Mix well then push 2 sprigs of mint into the liquid. Scrub and scrape the carrots, or peel them if you insist, then grate them coarsely and add to the dressing. Peel the remaining 2 oranges and cut into segments; be ruthless about cutting away all traces of pith and the membrane that divides one segment from the next. Remove pips (seeds) with the tip of a knife and add the oranges to the salad bowl. Mix all the ingredients together gently, then cover the salad and set it aside for 2 hours or a little longer to allow flavors to blend and develop. Close to serving time, remove and discard the tired sprigs of mint, stir in the walnuts and scatter with fresh torn mint leaves.