Preheat the oven to 325 degrees. Spray the jars with cooking spray.
In the bowl of an electric mixer, preferably fitted with a paddle attachment, beat the bananas until smooth. Add the eggs and beat until fully incorporated, scraping down the sides of the bowl as needed. Add the almond butter, almond flour, coconut oil, honey, vanilla, baking powder, baking soda, and salt. Beat until all ingredients are fully incorporated, scraping down the sides of the bowl as needed. Stir in the chopped walnuts.
Fill the jars half full with the batter, making sure to wipe the top of the jars clean of any batter. Place the jars directly on the rack of the oven and bake for 40 to 45 minutes or until a toothpick inserted into the center comes out mostly clean.
While the bread is baking, place the lids and rings for the jars into boiling water and let boil for 3 minutes. Remove from the boiling water, let cool, and dry well.
When done baking, remove the jars from the oven and place on a counter. Top with the lids and rings and let cool. The jars will seal as they cool. Once completely cool, eat immediately or store in the refrigerator for up to one week.