01 - Preheat the oven to 425°F. Line a large baking sheet with parchment paper.
02 - Remove leaves and trim the base of each cauliflower head, keeping the core intact. Slice each head into 1-inch thick steaks, yielding 2 to 3 steaks per head. Reserve loose florets for other uses.
03 - Place cauliflower steaks on the prepared baking sheet. Whisk together olive oil, cumin, smoked paprika, garlic powder, salt, and black pepper in a small bowl. Brush both sides of the steaks evenly with the marinade.
04 - Roast the cauliflower for 20 minutes, flipping halfway through, until golden and tender.
05 - Combine harissa paste, lemon juice, and maple syrup or honey in a small bowl, stirring until smooth.
06 - Remove the cauliflower from the oven and brush generously with the harissa glaze. Return to the oven and roast for an additional 5 to 7 minutes until caramelized.
07 - Transfer cauliflower steaks to plates, garnish with chopped parsley, and serve immediately.