Slice the yellow onion into 1/2-inch thick rings and carefully separate the layers.
In a medium mixing bowl, whisk together the chickpea flour, whey protein isolate, smoked paprika, garlic powder, sea salt, and black pepper.
Slowly pour the light beer and the egg white into the dry ingredients, whisking continuously until a smooth, thick batter forms.
Preheat your air fryer to 375°F and lightly brush or spray the basket with avocado oil.
Dip each onion ring into the protein batter, ensuring it is fully coated, and let any excess batter drip off before placing it in the air fryer basket in a single layer.
Air fry the rings for 10-12 minutes, flipping them halfway through the cooking time, until the exterior is crisp and golden brown.
While the onion rings cook, stir together the Greek yogurt and lemon juice in a small bowl to create a bright, high-protein dipping sauce.
Serve the onion rings immediately while hot and crunchy with the yogurt sauce on the side.