Preheat air fryer to 300 degrees F. Spray a 6-inch soufflé dish with nonstick cooking spray; set aside.
In a medium bowl, beat together the eggs, milk, hot sauce, garlic powder, salt, and black pepper.
Fold in the bread cubes, spinach, bell pepper, onions, and ¼ cup cheese. Stir to coat, making sure bread cubes are fully submerged.
Pour egg mixture into prepared casserole dish and transfer dish to the air fryer basket.
Cook for 20 minutes. Pause the machine, top with remaining cheese, and cook for an additional 5 minutes or until eggs are completely set and the edges are golden brown.
Carefully remove from fryer basket and allow to rest for 10 minutes before serving.