Preheat the oven to 350°F and grease a 9-by-13-inch baking dish.
Whisk the baking blend, baking powder, cinnamon, ginger, cloves, salt, and sweetener in a large bowl.
Add the zucchini, water, egg whites, Greek yogurt, softened butter, eggs, vanilla, and maple extract; mix until even.
Spread the batter in the dish and bake for 45 minutes, until the center is set but still moist; cool completely.
Brown the frosting butter in a skillet, stirring often, then cool for several minutes.
Beat the cream cheese, Greek yogurt, vanilla, molasses, and sweetener, then beat in the browned butter.
Frost the cooled cake, chill until firm, and cut into 15 servings.