Rinse lemon. With a vegetable peeler, pare yellow skin from lemon and finely chop. With a knife, cut off and discard white pith. Coarsely chop lemon, discarding seeds. In a 1- to 2-quart pan over high heat, bring to a boil 1 cup water, lemon peel, chopped lemon (with juice), dried apricots, sugar, minced fresh ginger, coriander seed, mustard seed, and hot chili flakes. Reduce heat, cover, and simmer for 5 minutes. Uncover and boil over medium heat, stirring often, until most of the liquid is absorbed, 10 to 12 minutes. Add salt and lemon juice, to taste. Cool. Serve or cover and chill up to 3 days.