Whisk together olive oil/chive drizzle ingredients and set aside.

To prepare fish marinade, cook mirin and wine in a small saucepan over medium heat until reduced by half; stir in miso paste and water with a wooden spoon until dissolved.  Increase heat to high and add sugar.  Cook, stirring constantly, until sugar is dissolved.  Add chile powders and let cool completely.  Place fish and marinade in a glass dish; cover and refrigerate for several hours or overnight.

Just before cooking fish, peel onions, leaving the base intact; cut each into 6 wedges.  Lightly toss with vinegar and oil in a medium bowl and season with salt and pepper.  Grill over high heat and cook until nicely charred; place back in bowl and cover with plastic wrap.  Let stand for 10 minutes to soften; set aside.

Remove fish from marinade and blot dry with paper towels.  Coat with oil and cook on a well-cleaned and oiled grill over medium heat until until well-marked and tender on one side. Transfer to a piece of heavy duty foil placed over indirect heat.  Cook for about 13 minutes.

While fish is cooking, stir together preserves and water and press through a fine mesh sieve; brush over fish and cook for 2 minutes more.  Brush peach preserve mixture over nectarine slices and grill until well-marked and tender.  Toss all salad ingredients together in a large bowl with grilled onions and nectarines.  Place equal amounts onto 4 serving plates and top with fish. Drizzle with olive oil/chive mixture and sprinkle with chives.