Prep a muffin tray with muffin liners or grease well, and set aside.
In a medium bowl, sift in the whole wheat flour. Add in oat bran, sugar, baking powder and salt. Whisk well and set aside.
In a large bowl, add in your bananas and mash them up if you have not already done so with your whisk or the back of a fork. Add in one egg and mix well. Add the milk, water, vanilla extract and lemon juice and beat the mixture well.
Add the dry ingredients to the wet, first using a whisk to incorporate the batter. Switch to a spatula or a wooden spoon and mix the batter. DO NOT OVERMIX.
At this point, you can fold in your add-ins. I added in cranberries and walnuts, but you could probably do any other combination of fruits/nuts.
Spoon the mixture into your greased/lined muffin tins. Bake in your preheated oven until a toothpick to the center comes out clean, or the tops are golden brown (but not burnt!), approximately 20 minutes.