In plastic zipper-top bag, place chicken. Add lemon juice, lemon zest, wine, oregano, salt and pepper; toss and turn bag to blend. Marinate chicken in refrigerator overnight or for several hours. Bring to room temperature before cooking.
In large skillet over medium-high heat, warm olive oil and butter. Remove chicken from marinade, reserving marinade to make the sauce. Place chicken in skillet and cook, turning once, until lightly browned on both sides, about 4 minutes per side. Transfer chicken to platter and set aside.
To same pan, add onion and tomatoes; reduce heat to medium and cook, stirring frequently, 2-3 minutes, until onion is soft and translucent and tomatoes soften and release liquid. Add garlic and sauté for 1 minute more. Add reserved marinade; bring to a boil. Reduce heat and simmer 2-3 minutes, until liquid is reduced by half.
Return chicken to skillet. Add olives and basil; simmer on low heat 3-4 minutes, until chicken is cooked through. Transfer chicken to platter or individual plates. Spoon sauce over each breast; scatter feta cheese on top.