01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or grease lightly with cooking spray.
02 - Combine diced strawberries and rhubarb in a medium bowl. Set aside while preparing the batter.
03 - In a large bowl, whisk together flour, granulated sugar, baking powder, baking soda, and salt until well combined.
04 - In a separate bowl, whisk eggs, vegetable oil, whole milk, and vanilla extract until smooth and fully incorporated.
05 - Pour wet ingredients into dry ingredients. Mix gently with a spatula just until combined. Do not overmix as this will result in dense muffins.
06 - Gently fold the diced strawberries and rhubarb into the batter, taking care not to crush the fruit pieces.
07 - Divide batter evenly among the prepared muffin cups, filling each about three-quarters full.
08 - In a small bowl, mix flour, brown sugar, cinnamon, and salt. Cut in cold butter using a pastry cutter or fingers until mixture resembles coarse crumbs.
09 - Sprinkle the streusel mixture evenly over the tops of the filled muffin cups, pressing lightly to adhere.
10 - Bake for 22 to 25 minutes until golden brown and a toothpick inserted into the center comes out clean.
11 - Allow muffins to cool in the tin for 5 minutes before transferring to a wire rack to cool completely.