Preheat the oven to 350°F, and coat 24 mini muffin cups with nonstick cooking spray.
In a small bowl, whisk together the flour, baking soda, baking powder, and salt. In a separate bowl, whisk together the butter or coconut oil, egg white, and vanilla. Stir in the buttermilk. Stir in the Greek yogurt, mixing until no large lumps remain. Gently fold in the diced peaches.
Divide the batter evenly between the prepared mini muffin cups. Bake at 350°F for 14-17 minutes or until the tops feel firm to the touch and a toothpick inserted into the center comes out clean. Cool in the pan for 5 minutes before carefully transferring to a wire rack.