Preheat the oven to 375 degrees F and grease a standard muffin pan with nonstick spray. (I use classic Pam spray.)
Add the butter, bananas, eggs, and vanilla to a large bowl. Stir to combine.
Stir in the flour, sugar, baking soda, and salt.
Gently stir in the diced strawberries.
Divide the batter among the prepared muffin tins, using about ¼ cup batter In each cup. Bake for 14-16 minutes, or until muffins are golden brown and a cake tester inserted into the center comes out cleanly.
Transfer muffins from the pan to a wire rack to cool.
Serve warm or at room temperature.
