Add Peppers and all Marinade ingredients to food processor. Process until well blended, about 20 seconds. Hold back 1/2 cup of Marinade to use as Salsa.
Add Marinade, Steak and Onions to a container or plastic baggie and place into refrigerator for at least three hours or overnight (which is best).
When ready to cook, preheat Air Fryer at 400 degrees for 10 minutes.
Remove steak from container/baggie and place into preheated Air Fryer.
Cook at 400 degrees for 6-8 minutes (for rare), turning over after 4 minutes. Add 1-2 minutes more for medium rare.
Remove Steak and Onions from Air Fryer and let rest for 5 minutes. Slice Steak at an angle against the grain and as thin as possible.
Serve in Tortillas with Pico de Gallo, Avocado, Shredded Cabbage, Cilantro and Lime Wedges or use for Steak Nachos.
Prepare the Sauce (no need to marinate) and add to cooking pot with the Onions. Sauté the onions for 2 minutes in the Sauce, add the meat and cook for 1 minute, with a 5 minute natural pressure release.
For rare Skirt Steak, hold back 1 Tablespoons of Brown Sugar and sprinkle it onto the meat, right before cooking.If Pasilla peppers are not readily available, try Poblano or Jalapeńo Peppers.