In a small bowl, mix together the Greek dressing ingredients. Pour half of the dressing on the chicken and marinate chicken for minimum 30 minutes.
Remove chicken & discard marinade. Grill the chicken over medium-high heat until internal temperature reaches 165 degrees.
In a large bowl, add the cooked orzo, red onion, black olives, tomatoes, bell pepper, and cucumber. Pour on as much of the remaining dressing as you like. Toss to mix well. Top with feta cheese.