Heat the oven to 325 degrees and line a sheet pan with parchment paper.
Add the mashed banana to a medium saucepan along with the organic sugar and coconut oil. Stir to combine. Cook over medium heat for 2 to 3 minutes, or until the pot comes to a sputtering boil. Cook for another 60 to 90 seconds, swirling the pan often so the mixture doesn’t burn.
Remove the pan from the heat, allow the sputtering to subside, then stir in the lemon juice, vanilla, cinnamon, nutmeg and salt. Fold in the flakes and nuts until combined.
Spread the mixture out on the prepared sheet pan in an even layer about 1/2-inch thick. Bake for 25 minutes, rotating halfway through, then remove the sheet pan from the oven and, using a butter knife, break the granola.
Bake again until the flakes are a deep golden brown, another 20 to 30 minutes, rotating and tossing halfway through so they don’t burn.
Remove the pan from the oven and allow the granola to cool completely, at least one hour. Transfer the granola to an airtight container and store at room temperature for up to a month.