Preheat oven to 350°. Combine hummus, feta cheese, diced tomato, and chopped kalamata olives. Cut a 1-inch-wide slit into the thick end of chicken breast halves, and carefully cut down to center of chicken to form a pocket. Divide cheese mixture evenly among pockets. Secure with wooden picks. Sprinkle chicken with salt and pepper. Heat a large ovenproof skillet over medium-high heat. Add olive oil to pan. Add chicken to pan; sauté for 4 minutes. Turn chicken over. Bake at 350° for 12 minutes; let stand for 5 minutes.