Prepare the grill for direct cooking over medium–high heat (230°C to 290°C).
Combine the rub ingredients. Brush the skirt steak pieces on both sides with the oil and season evenly with the rub.
Related Grill Skills
Preparing Skirt Steak
Combine the crema with the mayonnaise.
Gently warm the refried beans in a microwave oven for 1 minute at 50 per cent power. Stir in the salsa. Cover to keep warm.
Grill the steak over direct medium–high heat, with the lid closed, until cooked to your desired doneness, 4 to 6 minutes for medium rare, turning once. During the last 30 seconds to 1 minute of grilling time, toast the rolls, cut-side down, over direct heat. Remove from the grill and let the steaks rest for 3 to 5 minutes.
Spread the rolls on both sides with the crema–mayonnaise mixture. Spread a layer of the refried beans–salsa mixture on one side of each roll and a layer of mashed avocado on the other side. Cut the steaks across the grain into thin slices. Divide the sliced steak, queso fresco, jalapeño (if using) and cilantro evenly among the rolls. Serve warm.