Mix rub ingredients together in a small bowl. Coat the skirt steak with the rub mixture evenly and thoroughly
(Optional) Let the seasoned beef rest at room temperature for about 30 minutes
Preheat your grill to 400ºF
Sear both sides of the beef on your grill, about 4 minutes per side
After searing, move your beef to an elevated rack to finish cooking to desired doneness. (I like medium doneness on steak fajitas so I finish on the rack only for about 2 minutes)
Remove beef from heat and allow to rest for 10 minutes before slicing
Add onions and bell pepper to sauté pan with a splash of olive oil. Sauté veggies over medium heat for about 8 minutes or until they begin to soften
In a small saucepan, melt butter and mince garlic into the butter after butter has liquified (you can also melt the butter in the microwave if you prefer)
Alive the beef into thin slices, cutting against the grain
Serve immediately on warm flour or corn tortillas. Add veggies and avocado slices
Squeeze lime wedges over the steak and add garlic butter. Serve alongside optional toppings. Enjoy!