Preheat griddle to 350°F.
Add flour, baking powder, sugar, and salt to a large mixing bowl. Whisk together until well combined.
Place peeled bananas in a separate bowl. Use a fork to mash until smooth (no big lumps).
Add egg, milk, water, and vanilla extract to the mashed banana. Whisk until well combined.
Use a spoon to make a well in the center of the dry ingredients. Pour the banana mixture into the well, then pour the melted butter into the well (make sure butter isn't hot so that it doesn't cook the eggs).
Gently whisk together ingredients until just combined. Batter should be thick and lumpy, but no dry patches.
Melt a little butter on the hot griddle and use a spatula to spread it across the surface. Scoop out 1/4 cup of batter for each pancake and cook on the griddle for 2-3 minutes, until bubbles start to form and pop on the surface.
Carefully flip pancakes and cook another 1-2 minutes, until both sides are golden brown and pancakes are cooked through. Remove from griddle.
Repeat steps 7 & 8 with the remaining batter (only adding additional butter to the griddle as needed). Serve pancakes warm with butter, syrup, sliced bananas and walnuts if desired. Recipe makes about 16 pancakes.