Bring a large saucepan of water to the boil. Cook pasta according to packet instructions until al dente. Drain and reserve 1 cup pasta water.

Meanwhile, heat the oil in a large, deep frying pan over medium-high heat. Cook onion, stirring, for 2 minutes or until starting to soften, then add eggplant, parsley and garlic. Cook, stirring, for 5 minutes, then add ¹⁄³ cup water and cook for a further 5 minutes, or until eggplant is just tender. Add tomatoes and reserved pasta water and bring to a simmer. Add tuna and olives and reduce the heat to medium. Cook for 3 minutes, or until heated through. Stir in lemon zest and juice to combine. Season with freshly ground black pepper.

Serve with rocket leaves and drizzled with remaining oil.