In medium bowl, combine broth, sherry, oyster sauce and sugar; mix well. Add fish; stir gently to coat. Cover; refrigerate 15 to 30 minutes to marinate.
Drain fish, reserving marinade in small bowl. Add cornstarch to marinade; mix well. Set aside.
Heat oil in large skillet or wok over medium heat until hot. Add gingerroot, garlic and fish; cook and stir 3 to 5 minutes or until fish turns white. Remove fish from skillet.
Add onion to skillet; cook and stir 2 minutes. Add pea pods; cook and stir 4 to 5 minutes or until vegetables are crisp-tender. Add marinade mixture; cook and stir 1 to 2 minutes or until sauce is bubbly and thickened.
Gently stir in fish; cook until thoroughly heated. Place mixture on serving platter. Arrange tomato wedges around mixture.