Preheat the air fryer to 375°F (190°C). Give it 3–5 minutes so it’s hot when the food goes in. This helps with browning.
Prep the veggies. In a large bowl, toss the sliced peppers and onions with olive oil, Italian seasoning, garlic powder, salt, black pepper, and red pepper flakes if using.
Coat evenly.
Pierce the sausage links. Use a fork to prick each link a couple of times. This prevents bursting and lets excess fat render out.
Load the basket. Spread the peppers and onions in an even layer in the air fryer basket. Nestle the sausage links on top so they brown nicely.
Avoid piling too high; cook in two batches if needed.
Air fry for 8 minutes. This jump-starts the sausage and begins to soften the veggies.
Flip and stir. Turn the sausages, toss the peppers and onions, and spread everything back into an even layer.
Air fry for another 6–8 minutes. Sausages should be browned and cooked through, and vegetables lightly charred on the edges. Aim for an internal sausage temperature of 160°F (71°C) for pork and 165°F (74°C) for poultry sausage.
Finish with vinegar (optional). Toss the hot peppers and onions with a splash of balsamic or red wine vinegar to brighten the flavors.
Serve. Pile everything into toasted rolls with cheese, or spoon over rice or polenta. Taste and add a pinch more salt if needed.