Combine the ingredients for the marinade in a large shallow bowl or zip-top bag. Give it a taste to check for seasonings and adjust to preference. Coat the steak with the marinade and let sit covered in the refrigerator for at least 2-4 hours and ideally overnight (or see notes to freeze.) Remove from the refrigerator 30 minutes prior to grilling.
½ cup lime juice, ¼ cup pineapple juice, 2 tbsp Worcestershire sauce, 3 tbsp olive oil, 1 tbsp minced garlic, 2 tsp ground cumin, 2 tsp chili powder, 1 tsp kosher salt, 1 tsp smoked paprika, ½ tsp black pepper, ½ tsp red pepper flakes, ¼ cup chopped cilantro, 2 lbs skirt or flank steak