This recipe works with any firm, white fish, or you can use shrimp, scallops, lobster or clams. Some of the ingredients can be hard to find outside Asian markets or online, so I have substitutions below.
Mix all the marinade ingredients (except for the oil) together in a bowl. Really make sure each piece of fish is coated. Let this sit while you heat the oil up in a wok or pot. You want it at a full 350°F.
Fry the pieces of fish in batches, using a chopstick or butter knife to separate them as they fry. Fry until golden brown, then drain on a cooling rack set over a baking sheet. Let the oil cool a bit, then pour off all but about 2 or 3 tablespoons.
If you're not using a wok, move the oil to a big frying pan. Get the oil screaming hot over high heat on your biggest burner. The second it starts to smoke, add the ginger, garlic, green onions and chiles and stir fry about 30 seconds.
Mix the starch with the stock so you have a slurry.
Return the fish to the wok and add the bean paste, stock-and-starch mixture and stir fry 1 minute, or until the sauce looks glossy. Add the vinegar, soy sauce and Sichuan peppercorns and toss to combine. Serve at once.
Notes
If you can't find small, hot chiles like Thai or Chinese tsien tsin, use a serrano. You can reuse the oil by pouring it through a strainer to remove debris. It can be reused up to 4 or 5 times. Label it "fish oil."