Preheat the oven to 350°F. Melt coconut oil in a saucepan on medium-low heat. Add maple syrup, coconut, almond flour, and salt. Stir until everything is combined. Remove from heat. Add egg whites to the saucepan while stirring. Keep stirring for about 1 minute. The mixture should be quite sticky. Line a 9x13-inch baking dish with lightly greased parchment paper and pour in the mixture. Use your hands or a spatula to press down firmly. Bake for 10-12 minutes. Remove from oven.
While the crust is baking, beat the eggs and 2 egg yolks in a medium bowl with an electric mixer until frothy. Add the syrup, lemon juice, lemon zest, and almond flour. Beat for 2 minutes. Pour the mixture over the baked crust in the baking dish. Bake for about 16-19 minutes or until edges are light brown and the center is set. Let cool for at least 30 minutes before slicing. Cut into 2-inch squares. Dust with powdered sugar or coconut flour.