Preheat oven to 350 degrees. Line a large rimmed baking sheet pan with foil and spray with cooking spray (or a silpat mat or parchment paper). Puree banana in food processor or blender, (or using an immersion blender).
In a mixing bowl, combine pureed banana with the rest of the wet ingredients. Stir well. Add in the dry ingredients. Stir to combine then stir in pecans or walnuts if using. Spread mixture evenly on a baking pan.
Bake for 25 minutes, remove from the oven and break apart granola, stirring it around. Place it back into the oven for an additional 10 minutes. Let cool completely and enjoy, or place in airtight container for up to 7 days, or freezer for up to 3 months.