Heat the oil in a large pan over medium heat. Add the onion and ¼ teaspoon kosher salt, and cook over medium heat until soft and translucent, about 10 minutes (if the onion starts to brown, add a few tablespoons of water to the pan to prevent them from coloring). Add the minced garlic, ginger, cumin, coriander, mustard, turmeric, cayenne, and ½ teaspoon kosher salt and cook until fragrant, about 1 minute.

Add the chopped tomatoes, reserved tomato juice, and ½ cup water. Bring the curry to a boil, then reduce the heat and simmer until thickened, 15-20 minutes. Add the chickpeas and heat through.

Preheat the oven to 400° F. Line a rimmed baking sheet with foil.

Slice the cauliflower head into ¼-inch thick slices. Place the four center steaks on the baking sheet. (Reserve the rest of the cauliflower, which will be crumblier, smaller pieces, for something else.) In a small bowl, stir together oil, and turmeric. Drizzle spiced oil over cauliflower steaks and rub over to evenly coat, then sprinkle with kosher salt and freshly cracked black pepper.

Bake until the steaks are browned on the bottoms and the stalk portion of the steak is tender, 20-25 minutes.

Stir together yogurt, garlic, cumin, cayenne, kosher salt, and cilantro.

To serve, spoon some curry on the bottom of the plate and top with cauliflower steak. Drizzle with yogurt sauce and sprinkle with additional cilantro leaves.