Rinse the chicken and pat it dry with paper towels. Season to taste with salt and pepper.
Place the chicken breasts in a single layer in a glass baking dish. Place a rosemary sprig under each breast. Pour orange juice over the chicken. Cover and cook for about 12 mins, or until thermometer registers 165°F Be careful not to overcook. When done, arrange on serving platter, discarding rosemary.
Whisk the balsamic vinegar and orange zest into the cooking juices and adjust seasoning. Pour the sauce over chicken. Garnish with currants and walnuts.