Heat a cast-iron grill pan or skillet over high heat.
Place the steaks on a cutting board and drizzle the oil, then sprinkle them with salt and black pepper. Rub in the oil and seasonings with your hands to coat on both sides.
Cook the steaks for 3 to 5 minutes on each side, depending on how well cooked you like your steaks. Once cooked, transfer to a cutting board to rest for 5 to 10 minutes.
Meanwhile, prepare the chimichurri. In a small bowl, stir together all the chimichurri ingredients. Allow to sit for a few minutes while you finish the rest of the salad.
Assemble the salad. On a serving platter, arrange the baby salad leaves, tomatoes, radishes, avocado, red onion, cucumber, and flatbreads.
Top with the cooked steak, then drizzle with most of the chimichurri. Nestle a small dollop of the sour cream into the platter and drizzle a little more chimichurri on top before serving.
