Pour the vinegar into a shallow dish. Stir in the salt, pepper, oregano, and red pepper flakes.

Dip each tomato slice into the vinegar mixture. Preheat the air fryer to 360°F for 3 minutes.

Arrange the tomatoes, in a single layer, on a grill insert or directly in the air fryer (you should be able to cook 2 to 4 slices at a time, depending upon the size of your air fryer). To increase the cooking capacity, place a rack accessory over the grill insert or basket, which will allow for two layers of tomatoes to cook at once.

Spoon the remaining vinegar mixture over each tomato. Spritz the oil over the tomatoes. Cook at 360°F for 5 to 6 minutes. Remove the tomatoes carefully with a spatula.