In a medium skillet over medium heat, pour 1 tablespoon of olive oil. Once hot, add the minced garlic and sauté for about 1 minute, or until it becomes aromatic and golden.
Toss the chopped spinach into the skillet and cook for approximately 2-3 minutes, stirring often, until it wilts down. After cooking, remove the skillet from heat and allow the spinach mixture to cool slightly.
In a large mixing bowl, combine the wilted spinach with the ricotta cheese, grated Parmesan cheese, oregano, lemon zest, red pepper flakes (if using), and a sprinkle of salt and pepper. Stir until all ingredients are well incorporated and creamy.
Using a sharp knife, carefully make an incision in each chicken breast to create a pocket, slicing horizontally but being cautious not to cut all the way through.
Generously fill each chicken breast pocket with the spinach and cheese mixture, ensuring an even distribution among all breasts. If necessary, secure the openings with toothpicks to keep the stuffing inside.
Heat the remaining tablespoon of olive oil in an oven-safe skillet over medium-high heat. Once hot, place the stuffed chicken breasts in the skillet and sear them for about 3-4 minutes on each side, or until they achieve a golden-brown crust.
Once seared, transfer the skillet to your preheated oven and bake for 25-30 minutes, or until the chicken is thoroughly cooked and reaches an internal temperature of 165°F (75°C).
Carefully remove the skillet from the oven and allow the chicken to rest for 5 minutes. Remove any toothpicks before serving.
Notes
For a stunning presentation, serve with sautéed mixed vegetables or creamy mashed potatoes.