Trim skirt or flank steak and set aside.
Place dried ancho chile on a paper plate and microwave for about 15 seconds, until it smells toasty.
To a food processor or blender, add all marinade ingredients and process until smooth. Taste and adjust salt level as needed.
Pour half of the marinade into a large seal-able plastic bag, and pour the remaining half of the marinade into an airtight container and place in the refrigerator.
To the marinade in the bag, stir in about 1 1/2 tsp more salt, then add steak to the bag. Remove as much air as possible from the bag and seal. Move steak around in the bag to ensure it's well coated.
Marinate in the refrigerator for 3-4 hours, or overnight if preferred.
Preheat grill over high heat (covered), or preheat indoor grill pan over high heat (if grilling this steak indoors, you might want to turn the hood fan on and open a window or two to reduce smokiness). Oil grill or grill pan.
Remove container of leftover marinade to warm up to room temperature.
Pat steak slightly dry with a paper towel and place on the grill.
Cook steak for about 5-6 minutes per side, basting with additional marinade from the container, until steak reaches an internal temperature of about 135 degrees F for medium-rare, or until desired doneness.
Remove steak to a large cutting board, tent with aluminum foil and let rest about 5-10 minutes.
While steak is resting, add sliced peppers and onions to hot grill and grill for a few minutes, until tender and slightly charred.
Slice steak thinly, against the grain
, and serve with grilled peppers and onions.
Garnish with lime wedges, minced cilantro, sour cream, salsa, guacamole or avocado slices.
Serve as is, or wrapped up in flour or corn tortillas.