In a medium bowl, whisk or stir together the banh xeo crepe mix, coconut milk, 1 cup [2 cups] water, and ¼ teaspoon [½ tsp] salt until blended. Let stand while you prepare the rest of the meal.

• Trim the root end from the lettuce; separate the leaves and cut any larger leaves in half crosswise.
• Strip the mint leaves from the stems.
• Remove any coarse stems from the cilantro sprigs.
• Juice the lime.

In a small bowl, stir together the nuoc cham base, 2 tablespoons [¼ cup] lime juice, ¼ cup [½ cup] water, and as much sambal oelek as you like.

• Pat the pork dry with a paper towel. Cut the pork crosswise into ¼-inch-thick slices. Season generously with salt and pepper.
• Peel and thinly slice enough onion to measure ¾ cup [1½ cups].

In a large frying pan over medium-high heat, warm 2 to 3 teaspoons [1 to 2 TBL] oil until hot but not smoking. Working in batches if needed, add the pork and cook, stirring frequently, until browned but not yet cooked through, 2 to 3 minutes. Add more oil between batches if the pan is dry. Add the onion to the pan with all of the pork, season with salt and pepper, and cook, stirring occasionally, until the onion starts to soften and the pork is cooked through, 1 to 2 minutes. Transfer the pork and onion to a plate. Wipe out the pan.

• Trim the root ends from the scallions; thinly slice the scallions on the diagonal.
• Stir the crepe batter; add the scallions and stir to incorporate.

In the same pan used for the pork, warm 1 teaspoon [2 tsp] oil over medium-high heat until hot but not smoking. Spread half the pork mixture in the pan, then pour over half the batter. Gently tilt and swirl the pan to coat with a very thin layer of batter. Cook until the underside of the crepe is golden brown and crisp, 1 to 2 minutes. To check, carefully lift the edges with a spatula; if you can’t lift them, drizzle 1 teaspoon oil around the edges of the crepe. Cover and cook until the crepe is set, about 1 minute longer.
Sprinkle half the sprouts over the crepe. Using a spatula to loosen the sides, gently lift and fold the crepe in half and transfer to an individual plate. Repeat to make a second crepe, adding 1 teaspoon oil if the pan is dry. [Repeat to make 4 crepes total.]

On the plates with the crepes, arrange the lettuce leaves, mint, and cilantro on the side. Invite everyone to compose their own plates. To assemble, cut or tear the crepes into 2-inch pieces; nestle each piece inside a lettuce leaf and top with a few mint and cilantro leaves. Dip the stuffed lettuce leaves into the nuoc cham sauce and enjoy.