01 - Preheat the oven to 425°F. Line a large baking sheet with parchment paper.
02 - Remove the outer leaves from the cauliflower heads, keeping the stem intact. Cut each head vertically into 1-inch-thick steaks, aiming for 2 to 3 per head; reserve extra florets for another use.
03 - Place the steaks on the prepared baking sheet. Brush both sides with olive oil then season evenly with cumin, smoked paprika, garlic powder, salt, and pepper.
04 - Roast in the preheated oven for 25 to 30 minutes, flipping halfway through, until the steaks turn golden brown and tender.
05 - In a bowl, whisk together tahini, lemon juice, minced garlic, and salt. Gradually add cold water by tablespoon increments, whisking until the sauce is smooth and pourable.
06 - Arrange the roasted cauliflower steaks on a serving platter. Drizzle generously with tahini sauce, garnish with chopped parsley and toasted nuts if using, and serve with lemon wedges.