Put the garlic, chilli, oil, orange juice and oregano in a small bowl, mix well and season with salt.
Arrange the scallops in a single layer in a shallow bowl and pour over the garlic and chilli mixture. Cover and leave in the refrigerator to marinate for 15–20 minutes.
Wrap a strip of prosciutto around each scallop and secure with a metal skewer or presoaked bamboo skewer. Add a basil leaf and a sun-blushed tomato half to each skewer.
Position the skewers about 6 cm (2½ inches) away from a grill preheated to high and cook for 1–2 minutes on each side, or until the scallops have just cooked through. (Do not overcook or the scallops will become tough.) Remove from the grill and serve immediately.