Preheat the oven to 400 degrees F and grease a standard muffin tin well with nonstick spray.
Add the mashed banana, grated zucchini, milk, butter, eggs, and vanilla extract to a medium bowl. Stir gently with a spatula.
Add the flour, sugar, baking powder, and cinnamon. Stir gently to combine.
Stir in the blueberries gently.
Divide the batter among the prepared muffin tin. You'll use about a heaping ¼ cup in each muffin cup.
Bake for 22-28 minutes or until a cake tester inserted into the center comes out cleanly and the muffins are golden brown around the edges. Let cool in the pan for a few minutes, then transfer to a wire rack to cool completely, running a knife around the edges to loosen if needed.
Serve at room temperature, warmed slightly, or chilled.
