Slice the aubergine lengthwise and grill until soft. Roast the sweet potato until soft, peel and mash with the tuna, ricotta, lemon pepper and parsley. Place the tuna filling on the aubergines and roll to form the involitini. In a knob of butter sauté the shallot, garlic and lemon zest on low heat, add the lemon juice of one lemon, wine cream and simmer. Serve the involtini drizzled with the lemon sauce and with rocket leaves on top.