Arrange your fish steaks in one layer at the bottom of a heavy bottomed or stainless steel pot
Sprinkle fish sauce, shallot, garlic, chili flakes, salt and pepper on top of the fish. Cover and let rest for about 30 minutes.
Add oil to the fish and set on medium heat. In the meantime, make your caramel.
Make the caramel by heating sugar on high heat until it is a deep brown color. Be careful not to burn the sugar.
Add water to sugar and immediately pour mixture on top of fish.
Bring to a simmer and cook covered for 15-20 minutes. Check every few minutes and add boiling water as necessary if the liquid boils away too quickly.
Serve with white rice and pickled mustard greens.