Using a hand or standing mixer, mix the bananas, peanut butter, honey, and cinnamon/vanilla, if using, until very smooth.Add oats and nuts/seeds and mix until combined.Turn out onto a parchment covered baking dish. Press and flatten with a spatula until evenly distributed.Bake at 350 for 30 minutes, or until golden brown on edges.Allow to cool completely before cutting bars.Wrap in plastic wrap. Store at room temperature for a week or freeze for up to 6 months.