Preheat & Prep: Preheat the oven to 400°F. Chop spinach, green onion, parsley, dill, and mince garlic.
Make Filling: In a large bowl, mix together chopped spinach, minced garlic, crumbled feta, Greek yogurt, chopped green onion, parsley, dill, and cracked black pepper.
Slice Chicken: Place chicken breasts on a cutting board and pat dry with a paper towel. Make a horizontal slit in the thickest part of each chicken breast, creating a pocket without cutting through (about ¾ of the way).
Season Chicken: In a small bowl, mix oregano, paprika, garlic powder, onion powder, salt, and pepper. Rub the seasoning mixture over both sides of the chicken breasts.
Stuff Chicken: Fill each chicken pocket with the spinach and feta mixture, careful not to over stuff. Use toothpicks to secure the pocket by placing them along the seam to seal both sides together.
Sear Chicken: Heat a large cast-iron or oven-safe skillet over medium-high heat. Add a drizzle of olive oil and sear the chicken for 3-4 minutes per side or until a nice golden crust forms.
Bake: Transfer the skillet to the oven and bake for 15-18 minutes, or until the chicken reaches an internal temperature of 165°F.
Broil & Serve: If desired, broil the chicken for 1-2 minutes at the end for extra color. Let it rest for a few minutes and remove toothpicks before serving.