In the pan or bowl you plan to eat out of, add the tinned fish, squeeze in half of the lime, the mustard, if using, 3 or 4 grinds of black pepper, and mix to combine, breaking up the fish into large chunks. Top with a pinch of flaky salt, a drizzle of your nice olive oil, and fresh herbs, if desired. Adjust seasoning with more lime juice as needed.
Spread on toasted bread or crackers.