Preheat your oven to 350°F (175°C) and line a muffin tin with liners.
In a bowl, mash the bananas until smooth.
Add the egg, sugar, oil, and vanilla. Mix until combined.
In another bowl, whisk together flour, baking soda, baking powder, and salt.
Gradually mix the dry ingredients into the wet ingredients (don’t overmix).
Gently fold in the chopped strawberries.
Divide the batter evenly into muffin cups (about ¾ full).
Bake for 18–22 minutes or until a toothpick comes out clean.
Let cool for a few minutes, then enjoy warm!