In a large skillet/fry pan, heat the oil on medium high.
Carefully add the mustard seeds and allow them to pop.
Add the green chillies if using and the curry leaves and then add the shredded Brussels.
Toss the Brussels around in the oil, mustard seeds and the curry leaves.
Add the garlic, ginger, turmeric, cayenne powder, cumin and coriander.
Stir fry till fragrant and the Brussels sprouts are beginning to get tender.
Add the fresh coconut, if using.
You don't want to over cook; the colour should still be a vibrant green and the texture crisp tender.
Continue cooking until the texture is what you like, about 15 minutes or so for crisp tender.
Check the salt and season accordingly.
Stir through the cilantro before serving, if using.
Notes
You can use any neutral flavoured oil with high heat capability. The thinner you can hash/shred the Brussels sprouts, the quicker they will cook and become tender. If you have big pieces, you can cover the pan briefly to steam cook them slightly.