To prepare bottom layer, weigh or lightly spoon flour into a measuring cup; level with a knife. Combine flour and salt; stir with a whisk. Combine granulated sugar, egg substitute, ¼ cup melted butter, 2 tablespoons water, vanilla, eggs, and chocolate syrup in a medium bowl; stir until smooth. Add flour mixture to chocolate mixture, stirring until blended. Pour batter into a 13 x 9 inch metal baking pan coated with cooking spray. Bake at 350° for 23 minutes or until a wooden pick inserted in center comes out almost clean. Cool completely in pan on a wire rack.
To prepare mint layer, combine powdered sugar, ¼ cup melted butter, and next 3 ingredients (through food coloring) in a medium bowl; beat with a mixer until smooth. Spread mint mixture over cooled cake.
To prepare glaze, combine chocolate chips and 3 tablespoons butter in a medium microwave-safe bowl. Microwave at HIGH 1 minute or until melted, stirring after 30 seconds. Let stand 2 minutes. Spread chocolate mixture evenly over top. Cover and refrigerate until ready to serve. Cut into 20 pieces.