In a saucepan, bring vinegar, sugar, ¼ cup water, and 2 teaspoons salt to a boil over medium-high heat. Pour vinegar mixture over red onion. Cover and refrigerate for 2 hours or until ready to use.
In a large stockpot, combine pork belly, oregano, pepper, remaining 1 tablespoon salt, and water to cover. Bring to a boil over medium-high heat. Reduce heat to medium-low, and simmer until pork is tender, about 40 minutes. Drain, and pat dry. Let cool enough to handle, and cut into 2x1-inch strips.
Preheat air fryer to 400°.
In a large bowl, toss pork belly, Cajun seasoning, and baking soda until well coated.
Working in batches, place pork in air fryer basket. Set fryer to 400°, and cook until golden brown and crispy, 20 to 25 minutes, shaking basket occasionally and turning pork belly halfway through cooking. Serve hot with pickled red onions.
Recipe by Louisiana Cookin' at https://louisianacookin.com/air-fried-pork-cracklins-with-pickled-onions/