At least 8 hours prior to cooking, trim excess fat and silver skin from the skirt steak.
Juice both limes and zest one of the limes. Combine the lime juice, lime zest, Serrano (or Jalapeno) pepper, garlic, beef broth, and all seasonings in a sealable container.
Add the beef, turning to coat all sides. Marinate the beef for at least 8 hours or up to 24 in the refrigerator.
After marinating, sprinkle the steak with additional salt and pepper. Grill to desired doneness. Allow to rest 5 minutes before slicing against the grain into thin strips.
If grilling outdoors, create an aluminum foil pouch for the onions and bell peppers; heat until warm and tender (approximately 10 minutes). If using an indoor grill, grill the meat adding the sliced vegetables to the same pan for additional flavor.
Warm the tortillas in the oven or microwave according to the package directions.
Fill each with meat and vegetables. Top with a dollop of sour cream and serve.