For the stuffing, put the slices of bread into a bowl and pour over enough milk to completely wet them through. Place the wet bread into a fine sieve and set aside to drain for 4-5 hours, or preferably overnight, until the bread is moist but not wet. Squeeze out any excess milk before using.
Once the bread has drained, prepare the tomatoes. Make a small cross in the bottom of each tomato using a sharp knife. Prepare a large pan of boiling water and a large bowl of iced water. Add the tomatoes to the boiling water and blanch for 1-2 minutes. Drain and immediately add them to the bowl of iced water. When the skins of the tomatoes have loosened, remove the tomatoes from the water and peel away the skins. Cut each skinned tomato into quarters and remove the seeds.
For the vinaigrette, whisk all of the vinaigrette ingredients together until well combined. Season, to taste, with salt and freshly ground black pepper.
Sprinkle the quartered tomatoes with four tablespoons of the vinaigrette and set aside to marinate for at least 30 minutes.
Continue with the stuffing: blend the basil and parsley in a food processor with the olive oil until the herbs are finely chopped. Add the breadcrumbs, soaked bread, parmesan and garlic and pulse until the mixture comes together as a paste. Season, to taste, with salt and freshly ground black pepper.
To stuff the sardines begin by dividing the stuffing into 8 or 12 equal balls.
Place one filleted sardine onto a chopping, place one stuffing ball at the head end of the fish, and secure the fillets on either side of the stuffing ball using cocktail sticks so that the stuffing is inside the sardine. Smooth the stuffing that is still visible at the top and bottom of the fish using your fingertips. Repeat the process with the remaining sardines and stuffing balls.
Season the sardines with a little salt and freshly ground black pepper.
To cook the sardines, heat half of the olive oil in a large, non-stick frying pan over a medium to high heat. Fry half of the stuffed sardines until browned on one side, about 1–2 minutes.
Turn the fish over and fry for a further 1-2 minutes on the other side, or until the sardines are cooked through and golden-brown on both sides. Make sure the stuffing is heated through by inserting a sharp knife into the centre of the stuffing and testing the heat of the knife tip carefully with your fingertip.
Remove the sardines from the pan and set aside on a warm plate or in a warm oven.
Repeat the frying process with the remaining oil and stuffed sardines. When cooked, gently remove the cocktail sticks from the sardines.
Just before serving, drizzle two tablespoons of the vinaigrette over the rocket leaves and combine to coat the leaves. Arrange the marinated tomato quarters and the olives alternately around the edge of each of four serving plates.
To serve, place a handful of the dressed rocket into the centre of each of four serving plates. Divide the sardines equally among the four plates, stacking them on top of the rocket. Sprinkle with the chives. Spoon over the remaining vinaigrette.