Flake the tuna into a bowl and beat in the ricotta, spring onions, lime rind, dill, egg and salt and pepper to taste with a wooden spoon. Reserve 2 teaspoons of the lime juice and beat the remainder into the tuna mixture. Shape into 12 small cakes about 7 cm (3 inches) across.
Heat half the oil in a frying pan, add the fish cakes, in 2 batches, and cook over a medium heat for 4–5 minutes on each side until golden. Reduce the heat if they start to over-brown and cook for a further 1 minute. Remove from the pan with a slotted spoon and keep the cooked fish cakes warm in a preheated oven, 160° (325°F), Gas Mark 3, while you cook the remainder.
Meanwhile, whisk the remaining oil and lime juice together and toss with the rocket leaves in a bowl. Serve the fish cakes with the rocket salad and some garlic & herb mayonnaise (see below).