Preheat your oven to 400°F (205°C) and line a large baking sheet with parchment paper.
To cut the cauliflower into steaks, start by removing any green leaves from the base of the cauliflower. Them, use a sharp knife to trim the bottom of the stem so the head sits flat on your cutting board. Don’t remove the core entirely. The core is what keeps the florets connected. Place the cauliflower stem-side down, so it’s standing upright. This position allows you to make clean vertical cuts straight through the head.
Slice straight down through the center of the cauliflower head to cut it in half. Then, cut each half into 1-inch thick slices, working from the center outward. See notes.
In a small bowl, mix together avocado or olive oil, smoked paprika, garlic powder, oregano, salt, and black pepper.
Place cauliflower steaks on the prepared baking sheet and brush both sides generously with the seasoned oil.
Transfer to the preheated oven and tent with foil. Bake for 15-20 minutes, covered, then remove from the oven and gently flip each cauli steak over. Continue to roast uncovered for an additional 10–15 minutes, or until tender with crisp, golden edges.
(Optional) Prepare the homemade chimichurri sauce according to recipe instructions. For best results, let sit 10–15 minutes before serving.
Remove the fully cooked and tender cauliflower steaks from the oven and serve drizzled with chimichurri sauce, if desired. Best enjoyed immediately.