Beat egg yolks and the 1/2 cup sugar in a large mixing bowl with an electric mixer on high speed for 3 to 4 minutes or until thick and light. Beat in cooled chocolate and vanilla. By hand, stir in walnuts, bread crumbs, and cinnamon.
Wash beaters thoroughly. Beat egg whites in a large mixing bowl with an electric mixer on high speed until soft peaks form (tips curl). Gradually add 1/4 cup sugar, beating until stiff peaks form (tips stand straight). Fold about one-third of the egg whites into the chocolate mixture to lighten (chocolate mixture is very thick); fold in remaining egg whites. Line a 13 x 9 x 2-inch pan with foil. Lightly grease the foil. Spread mixture in prepared pan.
Bake in a 325 degree F oven about 25 minutes or until top is dry and toothpick inserted near center comes out clean.
Bring water and 1/4 cup sugar to boiling in saucepan; stir to dissolve sugar. Remove from heat; add Metaxa or brandy. Brush sugar syrup evenly over hot cake. Sprinkle with chopped walnuts, if desired. Cool completely. To serve, cut cake into 32 diamond shapes; place two diamonds on each serving plate. Garnish with chocolate-dipped apricot slices, if desired. Makes 16 servings.