For the Pickled Vegetables: Place the carrots and daikon radish in a medium heat-proof bowl. In a small saucepan, add the white vinegar, water, sugar, and salt. Bring to a simmer to dissolve the sugar. Pour the hot liquid over the vegetables and cool to room temperature. Cover and refrigerate until ready to use.
For the Marinated Pork: In a medium bowl or zip-top bag, add the scallions, garlic, sugar, fish sauce, sesame oil, soy sauce, POM Juice, lemongrass, and pork. Cover and refrigerate for at least 1 hour or overnight.
Adjust the oven rack to the position closest to the broiler and put the broiler on high.
Place a cooling rack inside of a baking sheet and place the pork on top. Season with salt. Broil, turning occasionally, until the pork is cooked to 145ºF, about 15 to 20 minutes.
To serve, spread mayonnaise on both sides of the rolls and top with sliced pork, pickled vegetables, cucumber ribbons, serrano peppers, POM Arils, and cilantro. Serve immediately.