Preheat oven to 350 degrees. Line a muffin tin with paper liners or grease well with oil or non-stick spray.
Add bananas, eggs, lentils, oil, maple syrup, milk, vanilla, and vinegar to a blender. Blend until smooth.
In a large bowl add flour, cinnamon, baking powder, and salt. Whisk to combine. Pour blender contents into the bowl then use a large spoon or rubber spatula to mix until well combined.
Use a portion scoop or spoon to divide the muffin batter evenly into the muffin tin. They should be filled to the top.
Bake until golden brown and cooked through (a toothpick inserted into the center of a muffin comes out clean), 18-20 minutes. Allow to cool for 5 minutes in the pan then transfer muffins to a cooling rack to cool completely.
Store muffins at room temperature for 2 days, in the fridge for 5 days, or freeze for up to 2 months.