Pat the steaks dry with paper towel and generously season with salt and pepper. Let sit overnight in the fridge or for 1/2 hour on the countertop. Either way, bring to room temperature before grilling.
To make the chimichurri, in a food processor, combine the parsley, cilantro, olive oil, garlic, red pepper flakes, black pepper and 1/2 tsp salt. Pulse until roughly chopped and the ingredients are combined. Scoop into a small bowl.
Heat your Spark to 500°F and brush the grill grates with oil. Place the steaks on the grill without moving until they easily release from the grill, about 5 minutes. Flip and cook on the other side for another 5 minutes. If using the Spark temperature probes, you'll want to aim for 125°-130°F for medium-rare. Remove from the grill and let rest for 10 minutes.
Slice the steak, drizzle a few spoonfuls of chimichurri on top and serve hot. Pass
the remaining chimichurri in a bowl on the side.