Preheat oven to 350 degrees. Line a 12 tin muffin pan with liners.
In a large bowl, mix together whole wheat flour, white flour, baking powder, baking soda, salt and zest of two lemons.
In a smaller bowl, mix together sugar, olive oil, eggs, buttermilk and the juice of one lemon (reserve the rest of the juice). Beat until all ingredients are combined.
Make a well in the dry ingredients and mix in the wet ingredients until combined. Make sure not to over mix.
Fill the 12 muffin tins with the batter.
Bake muffins for 18 to 22 minutes or until muffins are golden and toothpick stuck in the center of one comes out clean.
Cool for 10 minutes before removing to a baking rack.
Mix together remaining lemon juice from one lemon and powdered sugar until smooth. Brush the tops of the muffins with the mixture and sprinkle with the coarse sugar.