Fruit chutneys are terrifically handy for adding flavor and dash to so many dishes. This tropical version conveniently uses dried rather than fresh fruit. It's very quick to make and is great added to chicken salad, mixed into coconut rice, as a spread for ham sandwiches, or used as a base for crostini, topped with goat cheese, and broiled for an easy hors d'oeuvre.
Heat the oil in a medium-size saucepan over medium heat. Add the ginger, garlic, and mustard seeds; cook, stirring frequently, until the mixture is fragrant, 2 to 3 minutes.
Add the mango, pineapple, vinegar, sugar, salt, and 3/4 cup of water to the pan and bring to the start of a simmer. Reduce the heat to low, cover, and simmer until most of the liquid has been absorbed, 15 to 20 minutes. Cool and then refrigerate, covered, for up to 1 month.