Heat a large skillet over medium-high heat. Add oil and swirl to coat. Season chicken with salt and pepper and add to skillet. Cook until done, about 7 minutes. Remove chicken from pan and add bell pepper, oregano and garlic. Saute for 2 minutes. Add chicken and stock and cook for 1 minute. Remove from heat and add olives. Stir. Transfer to serving bowl or onto plates and sprinkle with feta cheese.