In a small bowl, combine chili powder, cumin, and cayenne. Mix well. Place halibut on a large plate. Brush both sides of fish with lime juice and sprinkle both sides with chili powder mixture. Let stand at room temperature for 10 minutes.
Meanwhile, spray a grill rack with cooking spray. Preheat a gas grill to medium or prepare a medium-hot fire in a charcoal grill, with the rack placed 4 to 6 inches above the heat.
In a medium bowl, combine black beans, salsa, green onion, and cilantro, and mix well. Set aside.
Place fish on the grill, cover the grill and cook for 10 to 14 minutes or until fish is opaque and flakes easily with a fork, turning once. Serve bean salsa with fish. Garnish with fresh cilantro.
Note: To broil halibut, place on a broiler pan and broil 4 to 6 inches from heat 10 to 14 minutes or until fish flakes easily with a fork, turning once.