Skin fish, if necessary. Rinse fish and pat dry. Rub both sides of fish with seasoned pepper. In a large nonstick skillet cook the fish fillets in hot oil over medium-high heat for 1 to 2 minutes on each side or until lightly browned. Reduce heat to medium-low. Carefully add margarita mix concentrate to skillet. Cook, covered, for 6 to 8 minutes or until fish flakes easily when tested with a fork. Serve fish and sauce with rice. Makes 4 servings.