Preheat the oven to 350 degrees Fahrenheit and line a 9 x 5-inch loaf pan with parchment paper.
Transfer the oats to a blender and blend for 20 to 30 seconds on high, until a flour forms.
Mash the ripe bananas in a large mixing bowl until they’re nice and creamy.
Mix the eggs, oil, vanilla extract, and lemon juice in with the mashed banana until the wet ingredients are well-combined.
Add the oat flour to the mixing bowl, along with any granulated sweetener you’d like to add, baking soda, sea salt, and ground cinnamon (the dry ingredients). Mix until well-combined and a banana bread batter forms.
Mix together the ingredients for the cinnamon swirl (coconut sugar or sweetener of choice) and ground cinnamon in a small bowl until well-combined.
Pour half of the banana bread batter into the prepared baking pan. Sprinkle all of the cinnamon sugar mixture over the banana layer evenly.
Pour the remaining banana bread batter over the cinnamon swirl layer and spread it into an even layer.
Use a butter knife to draw a large S shape into the batter. This is what creates the cinnamon swirl.
Bake on the center rack of the preheated oven for 40 to 45 minutes, or until the bread is golden brown on top and tests clean. You can insert a toothpick in the middle of the bread to test if it is baked through.
Allow the bread to cool for at least 40 minutes before slicing and serving.
Serve the bread warm with a pat of butter for the best results!