1) Preheat oven to 210 degrees C/Gas 6.
2) Whisk together the oil, mustard seeds, jalapeno, ginger, and turmeric in a small bowl.
3) Place cauliflower in a medium baking dish and toss with the flavored oil and season with salt. Roast until lightly golden brown and just tender, 20 to 25 minutes.
4) Serve hot.