Preheat oven to 350°F. Prepare Mini Whoopie Pie Pan with vegetable pan spray.
In large bowl, stir together flour, lemon zest, baking powder and salt.
In large bowl, beat butter and sugar with electric mixer until light and fluffy. Add egg white and vanilla extract; beat until well combined. Alternately add flour mixture and milk in three additions, beating until just combined. Spoon one tablespoon batter into each pan cavity.
Bake 9-11 minutes or until tops of cakes spring back when touched. Cool in pan 3 minutes. Cool completely on cooling grid.
For icing, whip water, meringue powder and 1/4 cup sugar in large bowl with electric mixer on high speed 5 minutes. Gradually add remaining sugar and continue whipping at high speed 5 minutes or until meringue is stiff and dry.
To assemble: Place one cake in bottom of treat pop. Pipe a layer of lemon curd. Pipe a swirl of meringue from back edge following the curve of the container, then filling in the center. Continue layering until treat pop is full. Top with swirl of meringue and, if desired, lemon zest.