Preheat your oven to 375°F (190°C). Prepare a standard muffin pan by lining it with paper liners or greasing it.

In a large mixing bowl, whisk together the all-purpose flour, sugar, baking powder, and salt until well combined.

In another bowl, beat the eggs and stir in the mashed ripe bananas, sliced strawberries, melted butter, and vanilla extract. Mix until blended.

Gently fold the wet mixture into the dry ingredients until just combined, being careful not to overmix.

In a small bowl, combine brown sugar, oats, cinnamon, and melted butter. Mix until crumbly.

Spoon the batter into the prepared muffin cups, filling each about 2/3 full. Top with crumb mixture.

Bake for 18-20 minutes or until lightly golden and a toothpick inserted comes out clean with a few moist crumbs.

Let muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.