1Heat coals or gas grill for direct heat. Carefully cut a horizontal slit in each chicken breast half, making a pocket when top of chicken is lifted back.
2Spread 1 tablespoon cheese inside each chicken pocket. Top with folded slices of prosciutto. Close chicken around filling, being sure that most of the filling is enclosed. Brush dressing on chicken.
3Cover and grill chicken 4 to 5 inches from medium-high heat 10 to 12 minutes, brushing occasionally with dressing and turning once, until juice of chicken is no longer pink when centers of thickest pieces are cut.