01 - Set the oven to 425°F and line a large baking sheet with parchment paper.
02 - Remove green leaves and trim stems of cauliflower heads, keeping cores intact. Slice each into two thick steaks about 1 to 1½ inches thick, reserving any loose florets for other uses.
03 - Arrange steaks on the baking sheet, brush both sides with olive oil, then evenly sprinkle with sea salt, black pepper, and smoked paprika if using.
04 - Roast for 20 minutes, then carefully flip each steak and continue roasting for an additional 10 to 12 minutes until golden and tender.
05 - Combine parsley, optional cilantro, garlic, oregano, olive oil, red wine vinegar, red pepper flakes, sea salt, and black pepper in a bowl. Stir well and let sit for at least 10 minutes to develop flavors.
06 - Plate the warm cauliflower steaks and generously drizzle with chimichurri sauce before serving.