01 - Preheat oven to 425°F. Line a large baking sheet with parchment paper.
02 - Remove the outer leaves from the cauliflower heads. Trim the stem ends, keeping the core intact.
03 - Slice each cauliflower head into 1-inch thick steaks (you'll get 2-3 intact steaks per head; save loose florets for another use).
04 - Place steaks on the prepared baking sheet. Brush both sides with olive oil and sprinkle evenly with smoked paprika, cumin, garlic powder, salt, and pepper.
05 - Roast in the oven for 25-30 minutes, flipping gently halfway, until golden and tender with crispy edges.
06 - In a medium bowl, combine parsley, cilantro, oregano, garlic, olive oil, red wine vinegar, and red pepper flakes. Stir well. Season with salt and pepper to taste. Let stand at room temperature to develop flavors.
07 - To serve, arrange roasted cauliflower steaks on a platter and spoon chimichurri sauce generously over the top. Serve immediately.