Stem and core cabbage and cut into 1/2-inch pieces. Heat the oil in a saute pan over medium-high heat until hot. Add the mustard seeds and cover the pan with a lid. When the spluttering of the seeds begins to subside, uncover and add cabbage. Sprinkle turmeric and red pepper, if you are using it, over the cabbage. Saute turning and tossing until the cabbage wilts. Stir in the salt and cover the pan. Lower the heat and steam cabbage in its own vapor until cooked, about 10 minutes. Uncover and toss in the coconut and cilantro.