First, poach chicken. Place chicken breast in a pan. Add water to cover.

Bring to a boil, then quickly reduce heat to low so that the water is barely at a simmer. Partly cover and gently simmer for 10 minutes.Turn off heat completely, and allow chicken to remain in hot water for 15-20 minutes.

Meanwhile, place lettuce, tomatoes, onion, and cucumber in a large bowl; toss to combine. Combine parsley with vinegar, mustard, oil, oregano, salt, pepper and garlic, stirring with a whisk.

Chop the chicken into bite-sized pieces. Spoon 1 tablespoon dressing over chicken; toss to combine

Add chicken mixture and remaining dressing to lettuce mixture; toss gently to coat.

Spoon about 2 3/4 cups salad onto each plate. Top each serving with 4 olive halves.