Cut leaves from around the cauliflower, and cut out the center core to create a flat surface for cauliflower to balance, making sure to leave the head intact.
Rub vegetable oil over cauliflower and season generously with salt. Transfer to a baking sheet or pie dish and roast for 45 minutes, or until fork tender.
Combine olive oil, lemon juice, grainy mustard, chili powder and cumin in a small bowl. Set aside until cauliflower finishes baking.
Remove cauliflower from oven and brush olive oil mustard mixture all over. Let rest 5 minutes, so the mixture can soak into the surface.
Sprinkle with chopped cilantro or other herbs, then cut into four pieces and serve hot.