-cut into 4 equal pieces While grill is heating, combine orange juice, vinegar and brown sugar in a large saucepan. Cook mixture, uncovered at a low boil until reduced to about 1/2 cup., about 20 minutes. Stir often as miixture cooks, to prevent scorching. Meanwhile combine oranges, tomato and onion in a colander or strainer and drain well. Transfer to a bowl, add cilantro and gently stir in all but 2 tablespoons hot orange juice syrup. Set aside. When ready to grill, rinse fish and pat dry. Brush both sides of the fish with the remaining orange juice mixture. Place fish on oiled grill over hot coals and cook, turning once, until fish is opaque in the center, 6-7 miinutes total. Remove from grill, transfer to serving platter and spoon relish over top.