Pat pork belly cubes dry and season with salt, black pepper, and garlic powder. Let sit for 10 minutes.
Preheat air fryer to 400°F. Arrange pork belly cubes in a single layer in the basket. Cook for 15-18 minutes, shaking basket every 5 minutes, until crispy and golden.
While pork cooks, whisk together maple syrup, soy sauce, apple cider vinegar, and red pepper flakes in a small saucepan. Simmer over medium heat for 4-5 minutes until slightly thickened.
Transfer cooked pork belly bites to a large bowl. Pour maple glaze over and toss until all pieces are coated.
Sprinkle with sesame seeds and sliced green onions. Serve immediately while hot and crispy.