Preheat broiler with rack set 4 inches away from heat. In a small bowl, stir together hoisin and honey; set aside.
Spray a baking sheet or broiler pan with cooking spray. Place salmon on sheet, skin-side down. Squeeze juice of half a lime evenly over salmon; season with salt and pepper. Place under broiler, and cook for 5 minutes. Remove from oven, and drizzle each fillet with 2 teaspoons hoisin mixture. Return to broiler, and cook until glaze is bubbling and salmon is cooked through, 2 to 3 minutes. Divide couscous evenly among 4 plates. Top each with salmon, and garnish with scallions and lime wedges. Serve immediately.