Preheat Your Oven: Preheat your oven to 425°F (220°C). Line a baking dish large enough to fit your cauliflower with parchment paper or lightly grease it.
Prepare the Cauliflower: Use a knife or kitchen scissors to remove the leaves from the cauliflower, keeping the core intact. Trim the stem slightly so it sits flat.
Mix the Seasoning: In a medium bowl, combine the olive oil (or broth/water), garlic powder, onion powder, smoked paprika, ground cumin, turmeric, chili powder, salt, and pepper. Mix well.
Season the Cauliflower: Place the cauliflower in your baking dish, top side up. Brush half of the spice mixture over the cauliflower.
Flip the cauliflower over, stem side up, and brush the remaining spice mixture on the bottom to evenly coat the entire head. (It's okay if a few white spots remain.)
Roast the Cauliflower: Bake the cauliflower, stem side up, uncovered, for 30 minutes. After 30 minutes, carefully flip it over to be top side up, and continue roasting for another 20 - 30 minutes, or until the exterior is browned and tender all the way through when pierced with a knife.
Make the Tahini Sauce: While the cauliflower is roasting, prepare the tahini sauce. In a bowl, whisk together tahini, lemon juice, maple syrup, garlic, salt, and pepper. Gradually add water, 1 tablespoon at a time, until you reach a hummus-like consistency. The sauce should be thick and spreadable, not runny.
Serve: Spread most of the tahini sauce on a serving dish (reserving 1-2 tablespoons of sauce). Place the roasted cauliflower on top of the sauce. Thin the remaining tahini sauce with 1-2 teaspoons of water if needed, and drizzle over the cauliflower. Sprinkle with chopped parsley or cilantro if using. Serve hot.