For the topping: Combine the cranberries, sugar, orange juice, ground ginger, and orange zest in a heavy small saucepan. Bring to a boil, stirring until the sugar dissolves. Simmer until the cranberries begin to pop, stirring occasionally, about 5 minutes. Remove from the heat and mix in the crystallized ginger. Cool slightly, then cover and refrigerate until cold. (Can be prepared 4 days ahead. Keep refrigerated.)
For the mousse: Combine the chocolate, water, and 3 tablespoons cream in a heavy medium saucepan over very low heat. Stir constantly until most of the chocolate is melted - be very careful to not overheat the chocolate or the cocoa butter will separate out. Transfer the mixture to a food processor and process until smooth. Cool to barely lukewarm.
Using an electric mixer, beat the egg whites in a large bowl until soft peaks form. Add ½ cup plus 3 tablespoons sugar and beat until stiff but not dry. Pour the lukewarm chocolate over the egg whites and gently fold together. Spoon the mousse into an 8-cup serving bowl or divide among 12 to 14 glasses. Cover and refrigerate at least 6 hours or up to 3 days.
Beat ¾ cup chilled cream in a medium bowl until very soft peaks form. Add 1½ tablespoons sugar and the vanilla and beat until soft peaks form. Spoon the whipped cream on top of the mousse, allowing a rim of chocolate to show. Top with the cranberries. (Can be prepared 1 day ahead. Cover and refrigerate.)