Preheat oven to 350 degrees. Brush a 9-inch springform pan with butter or oil on all sides; set aside.
In a medium bowl, whisk together the almond meal, polenta, and baking powder.
In the bowl of an electric mixer fitted with the whisk attachment, beat together the butter, and sugar until pale and fluffy, about 2 minutes. Reduce the mixer speed to medium; beat in the eggs, one at a time, scraping down the bowl as needed. Turn off the mixer and remove the bowl from the mixer. Use a spatula to fold in the dry ingredients and lemon zest. Fold until all of the ingredients are just combined.
Pour batter into prepared pan. It will be very thick, use a spatula or the back of a spoon to spread the batter to the edges of the pan. Bake until a cake tester inserted into the center comes out with just a few crumbs and the cake begins to pull away from sides of the pan, about 35-40 minutes.
Using a cake tester or skewer, prick holes all over the top of the warm cake; pour the glaze over the cake and let cool completely. Remove from pan and serve.