In a food processor, combine the parsley, cilantro, oregano, garlic, red wine vinegar, red pepper flakes, sea salt, and black pepper. Pulse a few times until finely chopped but not pureed. Scrape down the sides.

With the food processor running on low, slowly drizzle in the extra virgin olive oil until well combined and the sauce is emulsified. Taste and adjust seasonings as needed. Set aside half of the chimichurri sauce for serving and the other half for marinating the steak.

Pat the flank steak dry with paper towels. In a large mixing bowl or a resealable plastic bag, combine the steak with half of the prepared chimichurri sauce, lime juice, ground cumin, and chili powder. Massage the marinade into the steak to ensure it's fully coated. Marinate for at least 30 minutes at room temperature, or up to 4 hours in the refrigerator.

Preheat your grill or a cast iron skillet to medium-high heat. Lightly brush the grill grates or skillet with 1 tablespoon of olive oil.

Remove the steak from the marinade, letting any excess drip off. Place the steak on the hot grill or skillet. Cook for 5-7 minutes per side for medium-rare, or until it reaches your desired doneness (internal temperature of 130-135°F for medium-rare).

Transfer the cooked steak to a cutting board and let it rest for 5-10 minutes. Resting is crucial for juicy steak. Then, slice the steak thinly against the grain.

While the steak is resting, warm the corn tortillas. You can do this by heating them directly over a gas burner for a few seconds per side, or in a dry skillet over medium heat, or wrapped in foil in the oven, until pliable and warm.

Assemble the tacos: place a generous amount of sliced chimichurri steak into each warm tortilla. Top with diced or sliced avocado, a drizzle of the reserved chimichurri sauce, crumbled Cotija cheese, and finely diced red onion (if using).

Serve immediately with fresh lime wedges on the side for an extra burst of citrus.