Step 1: Pat the skirt steak completely dry with paper towels. Drizzle with 2 tablespoons of olive oil and rub all over. Season generously with 1 teaspoon of salt, 1/2 teaspoon of black pepper, 1 teaspoon of garlic powder, and 1 teaspoon of onion powder. Let the steak sit at room temperature for 15-20 minutes while you prepare the chimichurri and heat the grill.
Step 2: To make the creamy avocado chimichurri, combine the peeled and pitted ripe avocado, 1/4 cup fresh cilantro, 2 cloves garlic, 2 tablespoons lime juice, 2 tablespoons olive oil, 1/2 teaspoon of salt, and 1/4 teaspoon of black pepper in a food processor or blender. Blend until the sauce is smooth and creamy. Taste and adjust the seasoning if necessary.
Step 3: Preheat your grill to high heat, aiming for 450-500°F (230-260°C). Clean the grill grates thoroughly with a wire brush and then lightly oil them to prevent sticking.
Step 4: Place the seasoned skirt steak directly onto the hot grill grates. Grill for 3-5 minutes per side for medium-rare, or until it reaches your desired doneness. Use a meat thermometer to confirm internal temperature: 130-135°F (54-57°C) for medium-rare, or 135-140°F (57-60°C) for medium.
Step 5: Once cooked, transfer the grilled steak to a clean cutting board. Tent it loosely with aluminum foil and let it rest for 5-10 minutes. This crucial step allows the juices to redistribute, resulting in a more tender and flavorful steak.
Step 6: After resting, slice the skirt steak thinly against the grain. Arrange the sliced steak on a platter and generously spoon the creamy avocado chimichurri over the top. Garnish with crumbled feta cheese and chopped fresh parsley. Serve immediately with optional lime wedges.