Preheat your oven to 425 degrees F. Line a large rimmed baking sheet with parchment paper or brush it lightly with oil.

Stand the cauliflower upright on a cutting board and slice it from top to base into steaks about one inch thick. You should get three to four good steaks from the center of the head. The outer florets will crumble off as you cut. Save those florets and toss them onto the baking sheet too, they roast up just as well alongside the steaks.

In a small bowl, stir together 3 tablespoons of olive oil, the turmeric, garlic powder, and 1/2 teaspoon of the salt until combined. Brush this mixture generously over both sides of each cauliflower steak and over the loose florets. Lay everything in a single layer on the prepared baking sheet.

Roast for 20 minutes. Use a thin spatula to carefully flip each steak. The bottom should be deep golden brown with some caramelized edges. Return the pan to the oven and roast for another 10 minutes until the second side is golden as well.

While the cauliflower finishes roasting, make the tahini drizzle. In a small bowl, whisk together the tahini, lemon juice, warm water, and the remaining 1/4 teaspoon of salt. The mixture will seize up and look thick at first. Keep whisking and it will smooth out into a pourable sauce. If it is still too thick, add water one teaspoon at a time until it drizzles easily.

Transfer the roasted cauliflower steaks to a serving plate. Drizzle the tahini sauce over the top in a back-and-forth motion. Scatter the chopped parsley over everything if using. Serve warm.