Stir in a bit of Sambal Oelek or harissa at the end if you like a bit of spice in your curry and are not avoiding nightshades. This is excellent served with cauliflower rice.
Heat one tablespoon of avocado oil, in a sauté pan over medium heat and when hot, add the onion. Cook until the onion softens and caramelizes, 5-10 minutes. Add the spices and cook until fragrant, about one minute then add garlic and cook one minute more. Add the coconut milk, sweetener, and tamarind and bring to a boil. Reduce the heat to a simmer and cook until slightly thickened. Season to taste with salt and pepper.
Season fish with some salt and pepper and then add both the fish and bok choy to the sauce at a simmer and cook for 4 minutes, or until cooked through. Taste again for seasoning. Garnish with cilantro, if desired
Notes
You can substitute lime juice for tamarind paste but the tamarind does add a depth of flavor and is worth looking for. You can find it in the Asian section in most supermarkets.