Heat vegetable oil in a large pot over medium heat.
Add the onions and cook until softened about 5 minutes.
Add the garlic, ginger, turmeric, coriander, garam masala, and chilli powder. Cook for an additional minute, stirring constantly, to release the fragrance of the spices.
Add the pork and cook for a few minutes, stirring occasionally, until browned on all sides.
Add water, salt, and coconut slices (if using) to the pot. Bring to a boil.
Reduce heat to low, cover the pot, and simmer for about 1 hour, or until the pork is tender and cooked.
Once the pork is cooked, taste and adjust seasonings as needed.