In a small microwave-safe bowl, melt the butter (about 20 seconds).
In a pie plate, whisk together brown sugar and cinnamon.
Using a pastry brush, brush pineapple with melted butter, and toss pineapple into cinnamon sugar mixture. Press sugar lightly to adhere to the pineapple.
Place spears in a single layer* in the bottom basket of your air fryer.
Set air fryer to 400 degrees, and air fry the pineapple for 10-12 minutes until pineapple is heated through and the sugar is bubbling. Halfway through cooking, brush pineapple with any remaining butter.
Serve warm, as is, or top with ice cream or whipped topping! Also be sure to pour any of the juices that accumulate at the bottom of the air fryer on top of the pineapple. Enjoy!