To start, you’ll need a blender or food processor. Add the jalapeño, cilantro, garlic, lime juice, orange juice, vinegar, Worcestershire sauce, olive oil, brown sugar, cumin, salt, and pepper. Blend the ingredients together until you have a smooth, aromatic marinade. It’s a zesty mix that will tenderize the meat and infuse it with bold flavors.

Place your flank steak in a large dish or a resealable plastic bag. Pour the marinade over the steak, making sure it’s completely coated. Cover the dish or seal the bag securely and pop it in the fridge. For the best results, let the steak marinate for 4 hours, but if you’re short on time, even 1 hour will work wonders.

Preheat your grill to medium heat. Remove the steak from the marinade and discard any excess. Sprinkle a little salt and pepper on both sides of the meat. Place the steak on the hot grill and listen for that satisfying sizzle. Cook for 7–9 minutes per side, flipping once, until a meat thermometer reads 140–145°F for medium-rare. Remove the steak, cover it with foil, and allow it to rest for 5 minutes.

Slice the steak into thin strips, cutting against the grain for tenderness. Warm your tortillas on the grill or over an open flame until slightly charred. To assemble your tacos, start with a tortilla, add a few steak slices, drizzle generously with chimichurri sauce, and top with cotija, cilantro, and red onion.