Preheat your oven to 400°F (200°C).
Slice one large white onion into rings, approximately ¼-inch thick. Set the onion rings aside.
In a skillet over medium heat, cook 1 lb of lean ground beef until it is browned. Add one packet of zero-carb taco seasoning and ⅓ cup of water to the skillet. Stir the mixture and cook until the meat is fully seasoned and the liquid has evaporated, which should take about 5 minutes. Remove the skillet from the heat.
Lightly grease a 6-cavity donut pan with non-stick spray or butter to prevent sticking.
Begin by placing a layer of shredded Mexican cheese, about 1-2 tablespoons, at the bottom of each cavity in the donut pan.
Place an onion ring in each cavity, positioning it on top of the cheese layer.
Fill the center of each onion ring with 2-3 tablespoons of the cooked taco meat.
Top the onion rings with another layer of shredded Mexican cheese, about 1-2 tablespoons.
Place the donut pan in the preheated oven and bake for 20 minutes, or until the cheese is melted and golden brown.
Once baked, remove the donut pan from the oven and allow the onion rings to cool slightly before carefully removing them from the pan using a spatula or tongs.
Serve the onion rings immediately, pairing them with your favorite keto-friendly dipping sauce or adding toppings like jalapeños or chopped cilantro for extra flavor.
