01 - Preheat the oven to 425 degrees Fahrenheit. Line a baking sheet with parchment paper.
02 - Remove leaves and trim the stem of the cauliflower heads, keeping the core intact. Slice each head into 3/4-inch thick steaks, yielding 2 to 3 steaks per head. Reserve leftover florets for another use.
03 - Place the cauliflower steaks on the prepared baking sheet. Brush both sides with olive oil, then season with sea salt, black pepper, and smoked paprika if using.
04 - Roast the cauliflower steaks for 20 minutes. Carefully flip each steak, then roast for an additional 10 minutes until golden and tender.
05 - In a mixing bowl, combine parsley, cilantro, red wine vinegar, minced garlic, red pepper flakes, sea salt, and black pepper. Stir in the extra-virgin olive oil until fully incorporated.
06 - Arrange the roasted cauliflower steaks on a serving platter. Spoon the chimichurri sauce generously over the top. Serve warm or at room temperature.