Place egg whites in a medium mixing bowl and let stand at room temperature for 30 minutes. Meanwhile, cover a baking sheet with plain brown paper. Draw 6 3-inch circles on the paper. Set aside. Add vanilla and salt to egg whites. Beat with electric mixer until soft peaks form. Add sugar, 1 tablespoon at a time, beating at high speed for about 7 minutes or until very stiff peaks form. Fold in the cocoa powder.
Spread about 1 tablespoon meringue into a 3-inch circle on brown paper. Using a pastry bag fitted with a star tip (or use a plastic bag with a small slit cut in one corner), pipe remaining meringue around edges of circles, building up sides to form a shell. Bake in a 300-degree oven for 35 minutes. Turn off oven. Let shells dry in oven with door closed for 1 hour. Peel off paper carefully. Store meringues in airtight container.
Up to one hour before serving, spread 1 rounded tablespoon of yogurt in each shell. Chill. When serving, arrange fruit in each shell.
Melt the chocolate in a small plastic bag in microwave and drizzle over fruit. Or use ice cream just before serving and drizzle with the chocolate. Makes 6 servings.