In a food processor, combine the parsley, cilantro, garlic, red wine vinegar, dried oregano, red pepper flakes, salt, and black pepper. Pulse until the herbs and garlic are finely chopped but not a paste, scraping down the sides as needed.

With the motor running on low, slowly drizzle in the extra-virgin olive oil until the sauce is well combined and emulsified. Taste and adjust salt or vinegar if needed. Set aside at room temperature.

Pat the steak dry with paper towels. Season generously on both sides with the kosher salt and black pepper.

Heat the olive oil in a large cast-iron skillet or heavy-bottomed pan over medium-high heat until it shimmers. Carefully place the steak in the hot skillet.

Sear the steak for 3 to 5 minutes per side for medium-rare (internal temperature 130 to 135 degrees F), or until your desired doneness. Avoid moving the steak too much to develop a good crust.

Transfer the steak to a cutting board, tent loosely with foil, and let rest for 5 to 10 minutes. Then slice against the grain into thin strips.

In a large bowl, gently toss together the mixed greens, cherry tomatoes, diced cucumber, sliced red onion, diced avocado, corn, and black beans.

Divide the salad mixture evenly among 4 serving bowls.

Top each bowl with slices of the rested steak. Drizzle generously with the chimichurri sauce and serve right away.