Step 1: Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper.
Step 2: Prepare the cauliflower. Remove the outer leaves and trim the bottom stem, leaving the core intact. Place the cauliflower stem-side down on a cutting board and carefully slice into 1-inch thick 'steaks' from the center outwards. Any loose florets can also be roasted.
Step 3: Arrange the cauliflower steaks and florets on the prepared baking sheet. Drizzle with 3 tablespoons of olive oil. Season evenly with salt, black pepper, smoked paprika, and garlic powder.
Step 4: Roast for 20-25 minutes, then carefully flip the steaks. Continue roasting for another 15-20 minutes, or until deeply golden brown, tender, and slightly caramelized.
Step 5: While the cauliflower roasts, prepare the chimichurri. In a medium bowl, combine the finely chopped parsley, cilantro, minced garlic, and minced red chili (if using).
Step 6: Add the red wine vinegar, the remaining 1/4 cup of olive oil, dried oregano, and red pepper flakes (if using) to the herb mixture. Season with salt and pepper to taste.
Step 7: Stir everything together until well combined. Let the chimichurri sit for at least 10-15 minutes at room temperature to allow the flavors to meld.
Step 8: Once the cauliflower steaks are roasted, transfer them to serving plates. Spoon a generous amount of fresh chimichurri over each steak and serve immediately.