Preheat oven to 375°F (190°C) and line a 12-cup muffin tin with paper liners or grease with non-stick spray.
In a large mixing bowl, whisk together the all-purpose flour, rolled oats, sugar, baking powder, and salt until evenly distributed.
In a separate medium bowl, whisk the egg, milk, vegetable oil, and vanilla extract until well combined.
Create a well in the center of the dry ingredients and pour in the liquid mixture.
Stir using a spatula until just combined, ensuring no dry flour pockets remain; do not overmix.
Gently fold the diced strawberries into the batter until evenly dispersed.
Spoon the batter into the prepared muffin tin, filling each cup approximately three-quarters full.
Bake for 18 to 22 minutes, or until the tops are golden brown and a toothpick inserted into the center comes out clean.
Remove from the oven and allow muffins to cool in the tin for 5 minutes before transferring to a wire rack to cool completely.