Preheat the oven to 400 degrees F. Line a baking sheet with parchment paper.
While the oven heats up, make the chimichurri. Combine the parsley, cilantro, oregano and garlic in a food processor and pulse until small leaves and pieces remain. Add in the vinegar and pulse once more. With the processor going, stream in the olive oil and mix until just combined. Stir in a big pinch of salt, pepper and the red pepper flakes. Taste and season additionally if needed.
Stir half of the chimichurri into the greek yogurt. Keep the other half for drizzling. Set both aside.
Take 1 to 2 tablespoons of the finely grated manchego and place it in piles on the baking sheet, leaving about 1 to 2 inches in between each. Bake for 6 to 8 minutes, or until the manchego has melted and is bubbly. Cool completely on the baking sheet.
To make the steak, season it all over with salt and pepper. Heat a cast iron skillet over medium-high heat. Add the 2 tablespoons of butter to the skillet - it will begin to brown and smoke. That’s okay!
Place the steak in the skillet right away. Sear on each side, about 2 minutes per side, until deeply golden brown. Add the remaining tablespoon of butter if needed. Once you’ve done both sides, turn off the heat.
Place the skillet in the oven and cook for about 3 to 5 minutes, for medium doneness. This will depend on the thickness of your steak, but I suggest taking the internal temperature as this will help so much! For rare, you want 120 degrees F. For medium rare, 125 to 130 degrees F. For medium, 135 to 140 degrees F and medium-well, 145 to 150 degrees F. Remove the steak and let it rest for 10 minutes before slicing.
While the steak is resting, place the kale and onions in a large bowl. Add a few tablespoons of the creamy chimichurri and toss well, then massage the kale with the dressing using your hands.
Top the salad with the olives and the manchego crisps. Slice the steak and set it on top. Drizzle with the creamy chimichurri or the regular chimichurri - or both!
Serve!