Add the coconut milk, sugar, fish sauce (if using) and stir, then let the sauce reach a simmer.
Add the broccoli and mix, then wedge the fish fillets in between the broccoli and spoon over a bit of the sauce. Cover with a lid and cook until the fish is white and flaky.
Drizzle the lime (or lemon) juice evenly over the pan and season with some black pepper; taste and see if you'd like to add more seasoning or lime (lemon) juice.
Serve with rice and the optional toppings if you're using them.