Heat oil in a skillet over high heat. Add onion and garlic; cook and stir until fragrant, about 1 minute. Add pork; cook just until evenly browned, 2 to 3 minutes per side. Stir in soy sauce, water, peppercorns, and bay leaves. Reduce heat to low and cover stockpot. Cook until liquid is at a simmer, 1 to 2 minutes.
Uncover stockpot, add vinegar, and cook without stirring until vinegar dissipates and liquid thickens, 3 to 5 minutes. Stir in brown sugar and basil, cover stock pot, and cook until pork is tender and cooking liquid has thickened to sauce consistency, 10 to 15 minutes.