Lemongrass Pork Sandwich

In small bowl, stir lemongrass, shallot, fish sauce, brown sugar, and 1/4 teaspoon freshly ground black pepper until sugar dissolves. Transfer 2 tablespoons lemongrass sauce to small bowl; cover and refrigerate. Pour remaining sauce into large resealable plastic bag; add pork, turning to coat, and seal bag. You can marinate up to 1 day ahead.
Prepare outdoor grill for covered direct grilling on medium.
Meanwhile, in medium bowl, stir water, vinegar, sugar, and 1/2 teaspoon salt until sugar dissolves. Add shredded vegetables. If making ahead, refrigerate up to overnight.
Remove pork from marinade in bag; discard marinade. Place pork on hot grill. Cover and cook 20 minutes or until instant-read thermometer inserted into thickest parts of pork registers 155 degrees F, turning occasionally. Transfer pork to cutting board and let stand 10 minutes for easier slicing. If making ahead, wrap pork well and refrigerate up to overnight.
To serve, spread mayonnaise on rolls. Thinly slice pork and divide among rolls. Drizzle reserved lemongrass sauce over pork. Top each sandwich with 1/4 cup vegetable mixture, drained, jalapeno strips and 4 sprigs cilantro. Serve sandwiches with remaining drained vegetable mixture on the side.