Heat the oil in a large skillet over medium heat. Add the garlic and cook until fragrant, about 1 minute.
Add the pork and season with black pepper. Cook, stirring occasionally, until lightly browned on all sides, about 8 minutes.
In a small bowl, whisk together the fish sauce and sugar until the sugar is dissolved.
Pour the fish sauce mixture into the skillet. Bring to a boil and reduce heat to low. Simmer until the pork is tender and coated with a thick caramel glaze, about 15 minutes.