Preheat oven to 350 degrees Fahrenheit.

In a large mixing bowl, mix together the all purpose flour and baking powder.

In another large mixing bowl, whisk together the melted unsalted butter, sugar, egg. Then add the mashed banana, chia seeds, lemon juice/apple cider vinegar, and the milk, and combine into a thick batter.

Slowly stir 1/2 cup of the flour mixture into the banana mixture, and fold until the flour has been incorporated. Repeat for each 1/2 cup until the flour mixture is all folded in. Add walnuts into the batter.

Grease a 9x3x5 inch loaf pan (see Notes below to use other sized pans) with unsalted butter. Pour the batter into the pan or pans, and top with extra walnuts if desired. Bake for 50-60 minutes - then take a toothpick, and stick it in the center of each loaf. If it comes out clean (no batter attached) then the bread is done. If it has batter stuck to the toothpick, then I put the loaves back in the oven for an additional 5 minutes and test again.

When the bread is cooked through, remove from oven and allow to cool before slicing. Leftovers will keep for up to 3 days, or can be frozen for up to 3 months in a sealed bag.