Preheat your air fryer to 350 degrees F. Wash and dry the acorn squash, then use a sharp knife to cut it in half lengthwise. Use a spoon to scoop out the seeds, then discard them.

Brush the cut sides with olive oil, then season with salt and pepper to taste. Place the two halves of the squash, cut side down, in the basket of the air fryer. 

Air fry for 15 minutes. Carefully flip the squash, so the cut sides face up. Place 1 tablespoon of butter in the cavity of each one, then air fry at 400 degrees F for about 5-10 more minutes, until the squash flesh is browned and fork tender.