Clean the belt fish thoroughly and cut into 3-inch segments.
In a bowl, combine the fish with ginger slices, 2 tablespoons scallions, rice wine, salt, and white pepper. Mix gently and marinate for 15 minutes.
Remove the fish from the marinade and pat dry. Lightly coat each piece with cornstarch.
Heat cooking oil in a pan over medium-high heat.
Add the fish pieces and fry until both sides are golden brown. Remove fish and set aside.
In the same pan (leave about 1 tablespoon of oil), add minced ginger, minced garlic, minced scallions, and red chili pepper. Stir-fry until fragrant.
Pour in the chicken stock, soy sauce, dark soy sauce, oyster sauce, Chinkiang vinegar, and sugar. Stir to combine.
Return the fried fish to the pan. Bring the liquid to a boil, then cover and simmer on low heat for about 5 minutes to let the fish absorb the flavors.
Remove the lid and turn the heat to high to thicken the sauce slightly, coating the fish evenly.
Transfer to a serving plate and garnish with fresh scallions.