Step 1Heat oil in large pot over medium heat and saute carrots, leeks and fennel until tender, about 5 minutes. Add wine and stock, bring to a boil and simmer 3 minutes. Stir in parsley and mustard, cover and cook until vegetables are soft, about 5 minutes. Place chicken breasts over vegetables, add salt and pepper to taste, cover and simmer over low heat until chicken is cooked through, about 30 minutes.
Step 2Remove chicken breasts, wrap tightly and chill, reserving broth and cooked vegetables for timables.
Step 1Line 6 (1/2-cup) ramekins or custard cups with plastic wrap, overlapping about 2 inches. Set aside.
Step 2Bring 2 quarts lightly salted water to boil in large heavy pot. Stir in barley and simmer until tender, 30 minutes; drain well, transfer to medium bowl. Add diced vegetables, broth and salt to taste and mix well.
Step 3Heat olive oil in skillet over medium heat and saute zucchini until soft, 2 to 4 minutes. Transfer to a platter in a single layer. Arrange in an overlapping pattern on bottom and sides of prepared custard cups. Spoon in barley mixture and cover with overlapping plastic wrap. (There may be some barley left over, which can be eaten at room temperature as a salad.)
Step 4To serve, open plastic wrap from custard cup and invert onto lower half of serving plate. Remove plastic wrap and repeat with remaining custard cups.
Step 5Slice chicken breasts and arrange on serving plates and spoon poaching liquid over chicken breasts.