Combine the mint, basil, tuna and lemon zest in a large bowl and stir gently. Taste and season with sea salt and freshly ground pepper. Add the extra-virgin olive oil, if using.
Spoon generous portions of tuna onto the crackers or endive pieces. Garnish with lemon wedges, mint and basil sprigs. Serve immediately.
NotesCook's Note: For entertaining, the tuna can be diced in advance and kept well chilled in the refrigerator, then dressed when it's time to serve.