Thaw swai completely in the fridge.
Press hard between towels and let it air-dry for 10–15 minutes.
Marinate fish chunks with salt, Shaoxing wine, and egg white for 10 minutes.
Pat very dry with paper towels. Let sit 5–10 min.
Toss fish with cornstarch until just coated and shake off excess.
Rest 5 min on a wire rack.
Heat oil to 350–360°F and fry fish until just cooked and pale golden (2½–3 min).
Remove and drain well, then cool completely in a single layer on a rack.
If preparing to eat right away, skip to step 10.
Freeze fish pieces on a parchment-lined tray until solid (1–2 hours) and transfer to a freezer bag.
For the chili kit, freeze dried red chilies, Sichuan peppercorns, sliced ginger, and smashed garlic in a small freezer bag.
For the second fry, heat oil to 375°F and fry frozen fish for 2–3 minutes until golden and crisp.
Leave 2 tbsp oil in wok, heat until lightly smoking, then add peppercorns, fermented black beans, chilies, garlic, and ginger.
Add fried fish, toss hard, and sprinkle with sugar and MSG (if using).
Add scallions and kill heat after 10–15 seconds.
