Preheat the oven to 400 degrees . Line a 12-cup muffin pan with 1 1/4-inch paper liners. In a bowl, whisk the flour, baking powder and salt. In a large bowl, whisk the buttermilk, oil, zucchini, dill, feta and eggs. Add the dry ingredients to the wet mixture and fold until just barely blended.
Divide the batter among the liners (fill about three-quarters). Top each muffin with 2 zucchini slices and a sprinkle of pepper. Bake until puffed and golden brown and a toothpick inserted into the center comes out clean, 13 to 17 minutes. Cool in the pan.