Thaw fish if frozen. Rinse and pat fish dry with paper towels. Cut the fish into 1-inch cubes and discard any skin and bones; set aside.
Stir together undrained tomatoes, sugar, salt, and ground red pepper in a small bowl; set aside.
Heat wok or large skillet with cooking oil over medium-high heat (add more oil during cooking if necessary). Stri-fry onion and celery for 2 minutes in hot oil. Add sweet pepper strips to the vegetables and continue to stir-fry for about an additional 2 minutes more or until the vegetables are crisp-tender, and remove the vegetables from the wok.
Add half of the fish cubes to the wok and stir-fry for 3 to 5 minutes or until the fish flakes easily with a fork. Do not break up the pieces. Remove the stir-fry from wok and repeat with the remaining fish cubes. Remove all the fish from the wok.
Add the tomato mixture to wok and return the cooked vegetables to the wok. Stir all the ingredients together so vegetables are coated with the tomato mixture. Cook and stir the vegetables for about 3 minutes or until the mixture is slightly thickened.
Add parsley, then gently stir in fish. Cook the mixture for an additional 1 to 2 minutes or until the mixture is heated through.