Whisk together marinade ingredients (jalapeño through black pepper) until combined.
Add marinade to skirt steak in a single layer, turning to coat. Cover and refrigerate for at least 1 hr, but no longer than 8 hrs.
When ready to grill: preheat grill to medium-high. Grill steaks for 6-8 mins per side, turning once for medium-rare. Remove steaks and allow to rest for 5 mins.