1. To make the sauce, combine yogurt, minced cucumber, lemon juice, olive oil, garlic cloves, dill and salt in medium bowl. Stir well to combine. Refrigerate.
2. Preheat oven to 375 degrees. For the chicken, whisk together red wine vinegar, olive oil, garlic clove, oregano and rosemary in a medium sized baking dish. Add chicken breast, turning to coat. Cook in oven for 15-20 minutes or until chicken is done. Remove from oven and let cook. Slice into thin slices.
3. Assemble sandwiches: Spread sauce on each interior side of bread. Top with cucumber slices, chicken slices, pickled red onions and romaine lettuce.
1. The sauce can be made 1-2 days ahead and kept refrigerated.