Melt the coconut oil in a dutch oven or pot over medium heat, then add the mustard seeds. Once the seeds begin to splutter, add the onion, serrano pepper, curry leaves, and ginger. Cook for 5 minutes, stirring frequently until the edges of the onions begin to turn brown.
Add the salt, turmeric, cayenne, stir, then add the mango and chickpeas, stir again, then pour in the coconut milk.
Bring the pot to a simmer, then turn off the heat.
Serve hot or warm or room temperature.