Process fig spread, cilantro, lime zest and lime juice, garlic, chili flakes and scallions in food processor or blender until smooth. Heat glaze in small saucepan over medium heat until just bubbling, 2 to 3 minutes. Remove from heat and transfer ¼ cup glaze to small bowl to cool slightly. Stir butter into glaze remaining in saucepan, cover, and set aside.

Light large chimney starter filled with charcoal briquettes (about 100 coals); burn until coals are covered with fine gray ash, about 20 to 25 minutes. Pour coals over three-quarters of grill; set cooking grate in place, cover, and let grill heat up for 5 minutes.

Cut out four 12 by 8-inch rectangles of heavy-duty aluminum foil. Crimp edges of foil to create four trays that measure 7 by 5-inches with ½ inch sides. Coat trays with cooking spray. Season salmon with salt and pepper, brush each side of each fillet with 1/2 tablespoon reserved glaze (without butter), and place skinned side up on trays.

Place trays with salmon over hot fire and grill until glaze forms crust, 6 to 8 minutes. (Move fillets to cooler part of the grill if they darken too soon.) Using tongs, flip salmon and cook 1 minute. Spoon half of buttered glaze on salmon and cook until center of each fillet is still just translucent, about 1 minute. Transfer salmon to platter and spoon remaining buttered glaze over it. Serve.