Preheat oven to 425°F (220°C).
Remove leaves from cauliflower and trim the stem. Cut cauliflower into 1-inch thick steaks.
Mix olive oil, smoked paprika, garlic powder, salt, and pepper in a small bowl.
Brush both sides of cauliflower steaks with the seasoned oil.
Place cauliflower steaks on a baking sheet and roast for 20-25 minutes, flipping halfway through, until golden brown and tender.
While cauliflower is roasting, make the chimichurri sauce: Combine all sauce ingredients in a bowl and mix well.
Serve cauliflower steaks hot, topped with chimichurri sauce.