Preheat oven to 375 degrees F. Spray a 9x13 pan (I use a glass Pyrex dish) with cooking spray and set aside.
In a medium bowl, whisk together flour, baking powder, and salt. Set aside.
In a small bowl, combine granulated sugar and linme zest. Rub together with your fingers until fragrant.
In the bowl of a stand mixer, beat butter and and lime sugar mixture together until combined. Slowly add the powdered sugar and beat until light and fluffy, about 3 minutes. Add in the eggs, lime juice, and vanilla. Beat until smooth. Slowly add the flour mixture and beat until just combined.
Evenly spread the cookie dough into the prepared pan with a spatula. Bake for 12-14 minutes, or until the bars are slightly set in the middle. You don't want the bars to brown. Remove from the oven and let the bars cool completely.
While the bars are cooling, make the coconut frosting. In the bowl of a stand mixer, beat the butter until smooth. Add the lime zest, lime juice, vanilla, and coconut extract. Slowly add the powdered sugar, 1 cup at a time. Mix until smooth.
Frost the cooled cookie bars with coconut frosting. Sprinkle toasted coconut over the bars. Cut the bars into squares and serve.
Note-store bars in an airtight container in the fridge for up to 2 days.