Preheat oven to 200°.
To prepare meringue, cover a baking sheet with parchment paper. Draw a 9-inch circle on paper. Turn paper over; secure with masking tape. Place egg whites and salt in a large bowl; beat with a mixer at high speed until foamy. Add juice and vanilla; beat until soft peaks form. Add 3/4 cup sugar, 1 tablespoon at a time, beating until stiff peaks form.
Spoon egg white mixture into 9-inch circle on prepared baking sheet. Shape meringue into a nest with 1-inch sides using the back of a spoon. Bake at 200° for 1 hour. Turn oven off; cool meringue in closed oven for 30 minutes. Carefully remove meringue from paper.
To prepare topping, place chocolate and water in a small microwave-safe bowl. Microwave at high 1 minute or until chocolate melts, stirring every 20 seconds.
Arrange berries on top of meringue; drizzle with chocolate sauce. Garnish with mint sprigs, if desired.