Place a grill pan coated with cooking spray over medium-high heat until hot. Sprinkle pepper and salt over fish. Place fish in grill pan; cook 3 minutes on each side until medium-rare or desired degree of doneness. Remove from heat.
Combine broth, vinegar, sugar, soy sauce, and cornstarch in a small saucepan. Bring to a boil; cook 1 minute, stirring constantly. Spoon glaze over fish; top with green onions.