It's cooked almost dry with goraka (a sour dried fruit) and black pepper until the fish turns nearly black — a color born from a method meant to keep it edible for days with no ice.
Chunks of tuna or another firm fish are simmered in a near-dry paste of goraka, black pepper, cinnamon and curry leaves until the liquid cooks away and the fish darkens. It's sold by weight at family-run eateries and market stalls across Matara, Tangalle and the rest of the southern coast.