Preheat oven to 375°F (190°C).
Heat 1 tablespoon of olive oil in a skillet over medium heat and sauté minced garlic for 1 minute until fragrant.
Add chopped spinach to the skillet and cook until wilted, approximately 2 minutes; remove from heat and drain any excess moisture.
In a small mixing bowl, combine the wilted spinach, crumbled feta cheese, and dried cranberries.
Butterfly each chicken breast by slicing horizontally through the thickest part, stopping just before cutting all the way through.
Season both sides of the chicken breasts with salt, pepper, and dried oregano.
Place 1/4 of the stuffing mixture onto one side of each butterflied breast, fold over, and secure the edges with wooden toothpicks.
In an oven-proof skillet, heat the remaining 1 tablespoon of olive oil over medium-high heat.
Sear the chicken for 3 to 4 minutes per side until a golden-brown crust forms.
Transfer the skillet to the oven and bake for 12 to 15 minutes, or until the internal temperature reaches 165°F (74°C).
Allow the chicken to rest for 5 minutes and remove toothpicks before serving.