Greek Chicken with Tomatoes & Feta

From Fresh Everyday by Sarah Foster
4 boneless skinless chicken breasts (1½ pounds)
1 lemon, grated zest and juice
1 cup dry white wine
2 tablespoons chopped fresh oregano, plus more for garnish
½ teaspoon sea salt, plus more to taste
½ teaspoon freshly ground black pepper, plus more to taste
2 tablespoons olive oil
2 tablespoon unsalted butter
1 small onion, diced
4 plum tomatoes, cored and chopped
2 garlic cloves, minced
3/4 cup pitted Greek olives
6 fresh basil leaves cut into thin strips, plus more for garnish
2 ounces feta cheese cut into ¼ inch cubes, about ½ cup

Place the chicken breasts into a sealable bag. Stir the lemon zest and juice, wine, oregano, salt, and pepper together in a small bowl. Pour the marinade over the chicken and rub it onto all sides. Marinate the chicken in the refrigerator for several hours or overnight. Bring to room temp before cooking.
Heat the olive oil and butter in a large skillet over medium-high heat until the butter melts. Remove the chicken breasts from the marinade, reserving the marinade to make the sauce, and place them into the skillet. Cook the chicken breasts, turning only once, for 4 to 5 minutes per side, until lightly brown on both sides. Transfer them to a platter loosely covered with foil to keep warm while you prepare the sauce.
Add the onion and tomatoes to the pan you cooked the chicken in, reduce the heat to medium, and cook, stirring frequently, 2 or 3 minutes, until the onion is soft and translucent and the tomatoes soften and release liquid. Add the garlic and sauté for 1 minute, stirring constantly. Add the reserved marinade and bring it to a boil. Reduce the heat and simmer for 2 to 3 minutes until the liquid has reduced by half. Season with salt and pepper to taste.
Return the chicken to the skillet with the sauce. Add the olives and basil and simmer on low heat 6 to 8 minutes, until the chicken is cooked through and feels firm to the touch.
Transfer the chicken breasts to a platter or individual plates. Spoon the sauce over each breast and scatter the feta cubes over the top. Garnish with the additional fresh basil and oregano leaves, and serve warm.