Combine the rhubarb, brown sugar, lemon zest and juice, ginger, salt, and 1⁄4 cup water in a medium saucepan. Bring to a boil over high heat, then reduce the heat to medium-low and simmer for 12 to 15 minutes, or until the rhubarb mixture is thick. Remove from the heat, stir in the vanilla, then pour into a heat-safe bowl to cool completely.