- Preheat oven to 450 degrees Fahrenheit.
- Place the cauliflower head root-side down on a cutting board. Cut 2 (1-inch) slices in the center of the head. Add the remaining loose cauliflower florets to a medium bowl. Brush the steaks with 2 tablespoons of olive oil and add to a baking sheet.
- Drizzle a tablespoon of olive oil into the bowl with the remaining cauliflower. Season steaks and florets with salt and pepper. Add the florets to baking sheet.
- Bake for 20 minutes, flip everything halfway through. Meanwhile, whisk the harissa paste, lemon juice, lemon zest and remaining 1 tablespoon of olive oil together in a bowl.
- Drizzle the mixture over the cauliflower. Add back to the oven for another 10 minutes, or until the edges of cauliflower starts to crisp.
- Transfer the cauliflower to a serving dish and sprinkle with parsley. Serve warm.