Slice the fish into thin ¼ inch strips and add to a bowl.
Whisk the marinade ingredients together then pour over the fish. Marinate at least 5 minutes, or up to 30 minutes or 1 hour, refrigerated.
Heat 1 tablespoon vegetable oil in a wok or large pan to medium-high heat. Add the bean sprouts and stir fry for 1 minute. Remove and set into the bottom of serving bowls. This will support the fish.
Heat 1 more tablespoon vegetable oil (if needed) in the same wok or pan to medium-high heat. Add the chopped dried chilies and Sichuan peppercorns and stir fry until fragrant, about 1 minute. Transfer the stir fried chilies to a plate and set aside.
Add final tablespoon vegetable oil (if needed) and doubanjiang to the wok or pan and stir fry for 1 minute (doubanjiang will darken), then add garlic, ginger, green onion, fried dried chilies, and peppercorns. Stir fry 1 more minute.
Add water (or fish stock) and salt to taste. Simmer for 10 minutes.
Add marinated fish and simmer for 2-3 minutes (separating the slices, if needed), until cooked through. Transfer fish to serving bowls, on top of the bean sprouts.
Pour the soup/broth into the serving bowls.
Heat the wok back to medium-high heat. Add the hot chili oil and heat for 1 minute, or until it starts to sizzle.
Pour the sizzling hot chili oil over the serving bowls, then garnish wish spicy chili flakes and fresh chopped green onion. Serve sizzling hot!