Slice your chicken breasts through the middle, length-wise. Coat the bottom of a skillet with olive oil and place over medium-high heat. Add the thin sliced chicken. Season chicken with 1/2 teaspoon oregano, 1/2 teaspoon garlic pepper, and a touch of salt as it cooks. Allow to cook for about 3 or 4 minutes then flip and season other side with remaining seasonings. When chicken is thoroughly cooked and no longer pink in center, remove the pan from the heat and squeeze the juice from 1/2 lemon over the chicken. Transfer cooked chicken to a cutting board and set aside to cool.

Toast the walnuts in a shallow dish in a 350 degree oven for 5 minutes. Remove from oven and set aside.

Combine the pesto with the Greek yogurt.

Cook pasta according to package directions; rinse with cold water and drain well.  Transfer cooked and cooled pasta to serving dish. Add the pesto mixture and toss to combine. Add chicken, tomatoes, black olives and 1/2 cup crumbled feta (reserve remaining feta) and toss to combine. Sprinkle with toasted walnuts and remaining 1/4 cup feta. Serve immediately.