Combine mozzarella, shallots/scallions, tomatoes and basil in a small bowl.

Cut a horizontal opening along the front, long edge middle of each chicken breast, nearly through to the opposite side, to open like a book.

Spread the breasts with 2 teaspoons each of tomato paste. Divide the margarita cheese mix into 4 and place it in the center of each breast.

Close the breast over the filling, and secure the edges with a couple of toothpicks either side. Sprinkle the breasts with salt to season.

Heat oil in a large pan over medium heat. Add the chicken and cook until browned on one side (about 5 minutes). Turn the chicken over and fry for a further 5 minutes until browned.

Lower heat, cover pan and allow to cook until cooked through.