In a food processor, combine parsley, cilantro, garlic, red wine vinegar, dried oregano, and red pepper flakes. Season with salt and black pepper. Pulse until finely chopped, then gradually add olive oil while blending until well mixed.

Season both sides of the sirloin steak with salt and black pepper. Heat a skillet over medium-high heat with olive oil. Cook the steak for about 3-5 minutes per side for medium-rare.

In a large bowl, combine mixed greens, halved cherry tomatoes, chopped cucumber, sliced red onion, diced avocado, cooked corn, and black beans. Toss gently.

After the steak has rested, slice it against the grain into thin strips and place on top of the salad. Drizzle with chimichurri sauce before serving.