Peel & cut green mangoes into slices. If the mango is young and tender, cut through the entire seed and cut into quarters.
Place mango slices into a mixing bowl. Add li hing mui.
In a non reactive pot, combine vinegar, sugar, salt, garlic and peppercorns in a non-reactive saucepan and bring to a boil. When sugar and salt are dissolved, remove from heat and cool until it feels hot to touch (not scalding).
Pour over mangoes. Cover and let cool. Transfer to jars or storage container.