01 - Preheat the oven to 425°F. Line a large baking sheet with parchment paper.
02 - Remove green leaves and trim the stems while keeping the core intact. Slice each cauliflower head into two thick steaks, about 1 to 1½ inches thick. Reserve loose florets for other uses.
03 - Arrange steaks on the prepared baking sheet. Brush both sides with olive oil and evenly season with sea salt, black pepper, and smoked paprika if using.
04 - Roast for 20 minutes, then carefully flip each steak and continue roasting for another 10 to 12 minutes until golden brown and tender when pierced with a fork.
05 - While roasting, combine parsley, cilantro if desired, garlic, oregano, olive oil, red wine vinegar, red pepper flakes, sea salt, and black pepper in a bowl. Mix thoroughly and let rest for at least 10 minutes to blend flavors.
06 - Serve the roasted cauliflower steaks hot, generously drizzled with the chimichurri sauce.