Toss catfish with ¼ cup cornstarch, and set aside.
Add oil to a medium-size pan, and heat to 380° F.
In a small bowl, combine vinegar, soy, hoisin, water, sugar and 1 tablespoon cornstarch.
When oil is ready, carefully add catfish, and fry until golden and crispy. Remove from pan, and drain on paper towels.
In another saucepan, heat 1 tablespoon vegetable oil. Add ginger, chili flakes and garlic, and cook for 30 seconds. Add vinegar mixture, and cook an additional 30 seconds.
Add in cooked catfish, and toss to coat. Garnish with sliced green onion and additional chili flakes. Serve with rice.