Preheat your oven to 350°F (175°C) and prepare a donut pan by lightly greasing it.
In a medium bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.
In a separate bowl, mix the egg, buttermilk, vegetable oil, and vanilla extract until well combined.
Pour the wet ingredients into the bowl with the dry ingredients, stirring until just combined.
Gently fold in the chopped strawberries until evenly distributed.
Spoon the batter into the prepared donut pan, filling each cavity about halfway.
Bake in the preheated oven for 12-15 minutes or until a toothpick inserted in the center comes out clean.
Let the donuts cool in the pan for a few minutes before transferring them to a wire rack to cool completely.
