1. Heat 1 tablespoon of the oil in a large skillet over medium-high heat. Add the onion and cook, stirring frequently, until golden. Add the cauliflower, coriander, turmeric, and salt and pepper to taste. Cook for 2 to 3 minutes. Add the water and simmer until the cauliflower is tender and most of the water is absorbed, 3 to 5 minutes.

2. In a small skillet over medium-high heat, melt butter with the remaining 1 tablespoon olive oil. Add the mustard seeds and cook for 2 minutes.

3. To serve, transfer the cauliflower to a serving platter, drizzle with the mustard seed mixture and sprinkle with cilantro, if using. Serve hot.