Prepare the Chimichurri Sauce: In a bowl, combine chopped cilantro, parsley, minced garlic, red pepper flakes, red wine vinegar, 1/2 cup olive oil, and lime juice. Mix well and let it sit at room temperature for at least 15 minutes to allow the flavors to meld.
Season the Steak: Rub the flank steak with olive oil and generously season with salt and pepper on both sides.
Cook the Steak: Preheat a grill or grill pan over medium-high heat. Cook the flank steak for about 4-6 minutes per side, depending on thickness, or until it reaches your desired doneness. (Medium-rare is typically 130-135°F internal temperature).
Rest and Slice: Remove the steak from the grill and let it rest for about 5 minutes. Then slice it against the grain into thin strips.
Warm the Tortillas: In a dry skillet, warm the corn tortillas for about 30 seconds on each side until pliable.
Assemble the Tacos: Place a few slices of steak in the center of each tortilla. Top with a generous spoonful of chimichurri sauce, slices of avocado, diced tomatoes, and crumbled queso fresco.
Serve: Garnish with extra cilantro if desired, and serve immediately with lime wedges on the side.
Notes
Let the chimichurri sit for at least 15 minutes to enhance the flavors.