Fried-Fish Subs with Chili Sauce and Herbs

Pour enough oil into a small, heavy pot or Dutch oven to come a third of the way up sides. Heat over medium until a deep-fry thermometer reads 350°F, adjusting as necessary to maintain temperature. Meanwhile, in a medium bowl, whisk together fish sauce, lime juice, and chili sauce; season with salt and pepper. Add cucumbers, bell pepper, and serrano pepper, tossing to evenly coat. Let stand, tossing occasionally.

In a medium bowl, whisk together flour, cornstarch, baking powder, and 1/2 teaspoon salt. Whisk in seltzer just until batter is thin and bubbly with small lumps (do not overmix); set aside. Dredge shallots in cornstarch to evenly coat; shake off any excess. Fry until golden, 2 to 3 minutes. Transfer to paper towels.

Increase oil temperature to 360°. Working in batches, dredge fish in cornstarch to evenly coat; shake off any excess. Dip in batter, allowing excess to drain back into bowl, and gently lower into oil.

Fry, turning a few times, until fish is just cooked through and batter is golden and crisp, 5 to 7 minutes. Transfer to a wire rack set inside a rimmed baking sheet, lightly season with salt, and let drain and cool slightly.

Stuff rolls with fish, cucumbers and peppers, fried shallots, and herbs. Drizzle with pickling liquid and more chili sauce. Serve immediately.