Combine chocolate and water in saucepan; heat over low heat, stirring constantly, until melted and smooth. Cool until thickened; add vanilla. Prepare whipped topping mix as directed on package. Fold chocolate mixture into the whipped topping. Spoon into the prepared meringue shell. Chill for 2 hours before serving. Serves 6 to 8.
For meringue shell:
Beat egg whites with salt and cream of tartar until foamy. Gradually add sugar; continue beating until mixture forms stiff shiny peaks, about 10 minutes. Add vanilla and chopped pecans. Spread over bottom and sides of an 8-inch pie plate. Bake at 250° for 40 minutes; turn off heat and cool in oven for at least 1 hour, or overnight.