In a saucepan, combine Grand Marnier, jam, zest, vinegar, Worcestershire sauce, mustard, honey and red pepper flakes. Simmer over medium-low heat just until honey and jam are melted. Remove from heat; cool to room temperature.
Place chicken breasts, then marinade, in a zip-top plastic bag; marinate at least 4 hours and preferably overnight, refrigerated.
Preheat oven to 350°F.
Place chicken breasts in a shallow glass baking dish. Pour marinade over all. Baste breasts with apricot jam.
Cover loosely and bake 45 minutes to 1 hour, basting with remaining marinade every 15 minutes.