Preheat the oven to 450ºF.
Cut the onion into circular rounds about 1/4 inch thick.
Combine the almond flour, arrowroot powder, almond milk, garlic powder and nutritional yeast in once bowl. Mix the breadcrumbs and garlic powder in another bowl. (I suggest separating the breadcrumb mixture into 2 or 3 bowls because once you start dipping the onions and the breadcrumb mixture starts to get a little wet, it tends to stick together).
Taking one onion slice at a time, dip it first into the wet batter, covering it completely, then shake any excess batter off of it. Next, dip it into the breadcrumb mixture, and cover. Place on a lined baking sheet.
Continue to dip each onion slice in the wet batter first then the dry mixture, and place on the baking sheet.
Once all the onion slices have been coated, bake for 10 minutes. At the 10 minute mark remove the baking sheet from the oven and flip the onions, then place back in the oven for 5 more minutes. Onion rings should be golden brown at this point.
Let cool and then enjoy!