Heat grill. In small bowl, combine chili powder, garlic salt and cumin; mix well. Rub mixture on both sides of each tuna steak. When ready to grill, carefully oil grill rack. Place tuna on gas grill over medium-low heat or on charcoal grill 4 to 6 inches from medium-low coals. Cook 10 to 14 minutes or until fish flakes easily with fork, turning once or twice.