Preheat the oven to 375 degrees F (190 degrees C).
In a large bowl, stir together the oat flour, whole wheat flour, all-purpose flour, baking powder, salt and sugar.
Cut in shortening and 1/2 cup of butter until the lumps are smaller than peas. Stir in the lemon zest and poppy seeds. Make a well in the center and pour in the buttermilk. Stir just until the dry ingredients are moistened.
Divide the dough into 2 pieces. Pat each one into a 1 inch thick circle.
Cut circles into 6 wedges like a pie.
Place pieces onto a baking sheet, and brush the tops with melted butter.
Bake for 12 to 15 minutes in the preheated oven, until lightly browned. Cool on a wire rack so they do not get too crumbly.