In a medium bowl, whisk together lemon juice, lemon zest, minced garlic, olive oil, dried oregano, salt, and black pepper to create the marinade.
Place the chicken breasts in a large resealable plastic bag or shallow dish and pour the marinade over them. Seal the bag or cover the dish and refrigerate for at least 2 hours or overnight for best flavor.
Preheat the oven to 375°F (190°C).
Remove the chicken breasts from the marinade and place them in a baking dish. Reserve the marinade.
Bake the chicken breasts in the preheated oven for 20-25 minutes, or until the internal temperature reaches 165°F (74°C) and the chicken is cooked through.
While the chicken is baking, pour the reserved marinade into a small saucepan and bring to a boil over medium-high heat. Reduce heat and simmer for 3-4 minutes to cook off any raw chicken juices.
Remove the saucepan from heat and whisk in the chicken broth and unsalted butter until the sauce is smooth and slightly thickened.
Once the chicken is done, remove it from the oven and spoon the lemon sauce over the top.
Garnish with chopped fresh parsley before serving.