Preheat the oven to 400F. Grease a doughnut pan, and set aside.
Whisk together the flour, baking powder, and salt. Set aside.
Whisk together the egg and sugar until combined. Add the buttermilk, oil, and vanilla, and whisk until combined.
Add the dry ingredients, and mix until just combined. Do not overmix. Fold in the strawberries.
Spoon the batter into the prepared doughnut pan, filling almost to the top. Bake for 10 - 12 minutes or until a toothpick inserted comes out clean.
Allow to cool for 5 - 10 minutes before transferring them to a wire rack to cool completely.