Place the water in a small saucepan and sprinkle the gelatin over the top. Let the mixture sit for 1 minute to soften. Turn the heat to low and stir until the gelatin is dissolved. Remove from the heat.

Put the berries, sugar, lemon zest, and gelatin mixture in a food processor or blender and puree. Pour the mixture into a bowl, cover, and refrigerate for about an hour.

In another large bowl, whip the cream until it starts to thicken, then beat in the powdered sugar. Continue to beat until soft peaks form. Stir 1/4 of the cream into the strawberry mixture, then gently fold in the remaining cream. Cover and chill for at least 2 hours, or overnight.

To make the sauce, combine the berries, sugar, and lemon zest in a food processor or blender and puree. Pour this mixture into a saucepan and whisk in the cornstarch. Cook over medium heat, stirring often, until the mixture thickens. Remove from the heat and stir in the extract. Transfer to a bowl, cover, and refrigerate until cooled.

To serve, add some of the strawberry sauce to the bottom of a serving dish, then top with some of the mousse and more sauce, if desired. Top with whipped cream and serve cold.