Heat olive oil in a large pot over medium heat; cook pork and garlic in hot oil until the pork is completely browned, 7 to 10 minutes.
Stir brown sugar, soy sauce, fish sauce, and five-spice powder with the pork. Reduce heat to medium-low and cook mixture at a simmer, stirring occasionally, until the pork is tender enough to easily pull apart with a fork, about 2 hours.