Preheat your oven to 350°F (175°C). This ensures that your banana bread will bake evenly.
Grease your loaf pan with a little oil or line it with parchment paper for easy removal after baking.
In a medium mixing bowl, combine the gluten-free flour, baking powder, baking soda, salt, and cinnamon. Whisk them together until well mixed.
In a large mixing bowl, mash the bananas using a fork or potato masher until smooth. Add the vegetable or avocado oil, granulated sugar, brown sugar, eggs, and vanilla extract. Whisk until everything is well combined and smooth.
Gradually add the dry ingredients to the wet mixture. Using a rubber spatula, gently fold them together until just combined. Be careful not to overmix; a few lumps are perfectly fine.
Pour the batter into the prepared loaf pan, spreading it evenly.
Bake in the preheated oven for about 55-60 minutes, or until a toothpick inserted into the center comes out clean.
Once baked, remove the banana bread from the oven and let it cool in the pan for about 10 minutes. Then, transfer it to a wire rack to cool completely before slicing.