Thinly slice the onion using a mandoline or sharp knife to ensure uniform 1/8-inch rings.

In a shallow bowl, whisk together the coconut milk and apple cider vinegar. Add the onion rings, tossing to coat, and let soak for 15 minutes.

In a separate wide bowl, whisk together the cassava flour, arrowroot starch, sea salt, garlic powder, and onion powder.

Heat the avocado oil in a large deep skillet over medium-high heat until it reaches 350°F (175°C) or until a pinch of flour sizzles immediately.

Working in small batches, remove a handful of onions from the liquid, allowing excess milk to drip off, then dredge thoroughly in the flour mixture until fully coated.

Carefully place the coated onions into the hot oil in a single layer, ensuring the pan is not overcrowded.

Fry for 2 to 3 minutes, flipping occasionally with tongs, until the onions are golden brown and crispy.

Use a slotted spoon to transfer the fried onions to a plate lined with paper towels to drain excess oil.

Repeat the process with the remaining onions and salt lightly while still hot for maximum crispness.