Preheat oven to 350°F. Line a 9 x 13 x 2-inch baking pan with foil or parchment and spray the liner lightly with non-stick cooking spray.
In a medium bowl combine 1 1/2 cups all-purpose flour and 1/2 cup confectioners' sugar. Add 3/4 cup cold butter or margarine cut into small pieces and cut in with a pastry cutter, fork, or by pulsing in a food processor until the mixture resembles coarse crumbs.
Press the crumb mixture evenly into the bottom of the prepared pan to form the crust. Bake at 350°F for 15 minutes, or until the crust is set and lightly golden.
While the crust bakes, make the filling: in a large bowl beat together 4 eggs, 1 1/2 cups sugar, 1/2 cup lemon juice, and 1 teaspoon baking powder until smooth and well combined.
Remove the hot crust from the oven and immediately pour the egg-lemon mixture evenly over the crust. Sprinkle 1 cup flaked coconut evenly over the top.
Return the pan to the oven and bake at 350°F for 20–25 minutes, or until the top is golden brown and the filling is set (it may have a slight jiggle but should not be liquid).
Cool the pan on a wire rack until the bars are completely cool. Use the foil or parchment to lift the slab from the pan, then cut into bars.