Preheat the oven to 350 degrees. Line a baking sheet or jelly roll pan (10 inches by 15 inches) with parchment paper allowing paper to overhang by a few inches on both of the long sides of the pan (this allows lifting the pizza out of the pan).
Prepare the sugar cookie mix as directed on the package and add the lemon zest. Spoon into the prepared pan and press to fully cover the pan using a mixing spoon and fingers. Bake in the preheated oven until lightly golden (8-10 minutes). Note: every mix and oven is different so watch while baking and do not over bake. I removed mine at 11 minutes and it was not a true golden color but was cooked. Set on a cooling rack until it has fully cooled.
While the cookie is cooling, cut the strawberries. Cut into vertical slices about 1/8 inch thick. Cut away any green from the top. Using similar size strawberries will allow more uniform sizes stripes. Cover and place in the refrigerator.
Once the pizza ‘crust’ is cool, add the softened cream cheese into a mixer bowl and beat at high speed until fully creamed. Add the remaining ingredients and beat on medium to incorporate, raising the speed to high to beat into a creamy frosting. Note: it may appear lumpy during the beating process but continue until it becomes creamy.
Spread the frosting evenly to cover the entire cookie. If needed the cookie can be lifted from the pan by the parchment paper to do this step.
Place the blueberries in the top left corner. I made 6 rows of 8 blueberries (not correct for the number of stars on the actual flag but looked uniform), placing them close together but leaving space for the white to show through (refer to the photos).
Before adding the strawberries to the pizza I dabbed them with a paper towel to remove any excess moisture. To make the red stripes begin at the very top to the right of the blueberries laying the strawberries in a row, end to end, with all the slices going the same direction (e.g. tops to the right or to the left, just all facing the same direction). Leave about an inch of exposure white topping between each row of strawberries. Doing a bit of planning with a ruler will help make equally spaced rows or just do it freehand!
Once the flag is assembled, cover with plastic wrap and refrigerate until serving (especially on a hot day!). Cut into serving pieces with a sharp kitchen knife or pizza cutter.