1. Heat a grill pan over medium-high heat. Coat pan with cooking spray. Sprinkle chicken with salt and pepper. Add chicken to pan; cook 6 minutes on each side or until done.
2. Heat a large skillet over medium-high heat. Add oil to pan; swirl to coat. Add onion and garlic; sauté 4 minutes. Add olives and tomato; cook 3 minutes or until tomato begins to break down, stirring occasionally. Remove pan from heat; stir in parsley, oregano, and juice. Top chicken with tomato and olive mixture; sprinkle feta evenly over chicken.