For the prosciutto, heat the oil in a pan over a high heat. Add the prosciutto and fry for one minute on each side, or until crisp and golden. Drain on kitchen paper.
For the dressing, heat the oil in a frying pan over a medium heat. Add the onion and garlic and fry until soft.
Add the tomatoes and fry for 3-4 minutes, or until soft.
Add the chives and season, to taste, with salt and freshly ground black pepper.
For the salad, arrange the basil leaves onto a serving plate in a circle. Place half a cherry tomato cut-side up onto each basil leaf. Spoon a little of the dressing over each cherry tomato.
To serve, arrange the proscuitto in the middle of the plate and season with salt and freshly ground black pepper.