1. Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper or lightly grease a baking dish.
2. In a small skillet, heat the olive oil over medium heat. Add the minced garlic and chopped spinach, sautéing until the spinach is wilted, about 2-3 minutes.
3. Remove from heat and stir in the crumbled feta cheese, lemon zest, and oregano. Season with salt and pepper to taste.
4. Using a sharp knife, carefully cut a pocket in each chicken breast by slicing horizontally, making sure not to cut all the way through.
5. Spoon the spinach and feta mixture into each pocket, securing with toothpicks if necessary to keep the filling intact.
6. Place the stuffed chicken breasts on the prepared baking sheet. Brush each with melted butter and drizzle with lemon juice.
7. Bake in the preheated oven for 25-30 minutes or until the chicken is cooked through and the juices run clear. An internal temperature of 165°F (74°C) is recommended.
8. Let the chicken rest for a few minutes before removing the toothpicks and serving.

There’s a certain satisfaction that comes from seeing these stuffed chicken breasts transform in the oven, the filling peeking out as they bake to perfection. And remember, if a bit of feta spills out, it’s just an extra treat for the cook!