Preheat oven to 350°F (175°C) and line a muffin tin with liners or grease lightly.
In a bowl, mash the banana until smooth.
Add egg, melted butter (or coconut oil), Greek yogurt, and vanilla extract; whisk until combined.
In a separate bowl, whisk together flour, baking powder, baking soda, and salt.
Gently mix dry ingredients into the wet ingredients until just combined (don’t overmix).
Fold in the chopped strawberries.
Divide batter into muffin cups, filling each ¾ full.
Bake for 18-22 minutes or until a toothpick inserted in the center comes out clean.
Let muffins cool in the pan for 5 minutes, then transfer to a wire rack.