Zest the orange, and set it aside. Remove the outer pith and remove half of the segments. Reserve them for garnish.
Squeeze the juice from the remaining half of the orange into a baking dish.
Add the brown sugar and miso to the baking dish, then stir to combine. Remove one tablespoon of the miso-OJ mixture and set aside for the pesto.
Place the salmon flesh side down in mixture, cover, and refrigerate for at least 15 minutes.
Preheat the grill to 375 degrees.
While the grill is preheating, chop the orange zest and cilantro leaves (use a small food processor or a knife)
Add the reserved tablespoon of miso-OJ mixture to make a pesto.
Place the flesh side of the salmon onto the grill and cook for 4-5 minutes. Flip the fish and place the pesto on top. Cook for an additional 4 minutes. Remove the salmon from the grill and top with orange garnish.