In a mixing bowl, combine fish sauce, soy sauce, brown sugar, minced garlic, minced lemongrass, minced shallot, and black pepper to create the marinade.
Add the thinly sliced pork to the marinade, ensuring each piece is well-coated. Cover and refrigerate for at least 1 hour, or overnight for deeper flavor.
Preheat the grill to medium-high heat and lightly oil the grates. Grill the marinated pork slices for 2-3 minutes on each side, or until charred and cooked through.