4 boneless, skinless chicken breast halves |
2 tablespoons olive oil |
1 teaspoon grated lemon zest |
1/4 cup fresh lemon juice |
1/2 cup chicken broth mixed with 2 teaspoons cornstarch |
2 tablespoons chilled unsalted butter |
1 small scallion, thinly sliced |
salt and freshly ground pepper |