For the sea bass: Rinse the fish under cold running water and pat dry with paper towels. Cut some slits into both sides of each fish and sprinkle with salt and pepper. Stuff the slits with the ginger. Place each fish on separate heatproof plates (making sure that the plate and fish fit inside a large bamboo steamer). Dress each fish with 2 tablespoons of the wine.
Place each plate of fish in separate trays of your bamboo steamer. Stack and cover with the lid. Place the whole steamer basket over a wok that is three-quarters full with boiling water, making sure the water does not touch the base of the steamer. Steam until the fish is cooked through and the flesh flakes when poked with a knife, 8 to 10 minutes.
For the topping: While the fish is steaming, heat a second wok or large frying pan over high heat. When the pan is hot, add the peanut oil. Add the pancetta and cook for a few seconds. As they start to brown, add the five-spice powder. Toss in the mushrooms and ginger, then stir-fry for 1 minute, adding a touch of water to help the mushrooms cook. Add the wine and stir-fry for a few second then toss in the chestnuts. Add in soy sauces and mix well. Add the chile oil to taste. Toss to combine.
Carefully remove the fish on the plates from the steamers. To serve, ladle some of the stir-fried topping over the fish and garnish with the scallions. Serve immediately with soy sauce on the side.