Sauté onion and garlic over medium heat until the bottom of the pan has started to caramelize, about 5-7 minutes.
Add the mushrooms and allow their water to deglaze the pan. Add a splash of water if needed. Let their water cook off completely until the pan just start to caramelize again, then remove from the heat and allow the pan and veggies to sit and cool slightly to remove anything stuck to the bottom.
In the meantime, in a medium mixing bowl, mash your beans and combine them with all of your other ingredients except the oat flour and mix until well combined.
Add the veggies and oat flour and mix again until well combined. Your batter should be somewhat firm but not flakey; dry enough to hold it's shape. Add more flour 1/4 cup at a time as needed to get the right consistency.
Roll out your chickpea balls using ~2 tbsp per ball and place on a dry plate or baking tray so they aren't touching.
Preheat your oven to 350 degrees Fahrenheit and bring your clean, dry nonstick pan back over a medium heat. Sear each chickpea ball on all sides, rotating them in the pan with your fingers or a spoon or spatula [note#2] until each side is a golden brown.
Transfer your seared chickpea balls into your baking tray and bake for 20 minutes to cook them through.
Serve by themselves or with tomato sauce poured over the top, or serve them as a topping over a pasta of your choice.
Enjoy!