Preheat oven to 400 degrees F (200 degrees C). Butter 9x13-inch baking pan; sprinkle 2 tablespoons cornmeal on bottom. Sift all-purpose flour, semolina flour, 1/2 cup cornmeal, baking powder, and salt together in a bowl. Whisk spinach, buttermilk, feta cheese, eggs, and vegetable oil together in a separate large bowl. Stir flour mixture into spinach mixture just until pourable batter forms. Pour batter into prepared baking pan. Bake in preheated oven until a toothpick inserted into the center comes out clean, about 45 minutes.