Creating spinach stuffed chicken breasts is simple when you follow these easy steps:

1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Prepare Filling: In a mixing bowl, combine the chopped spinach, cream cheese, mozzarella cheese, Parmesan cheese, minced garlic, onion powder, salt, and pepper. Mix until well-combined and set aside.
3. Prepare Chicken: Place each chicken breast on a cutting board. Use a sharp knife to cut a pocket in each chicken breast by slicing them horizontally, being careful not to cut all the way through.
4. Stuff Chicken: Generously stuff each chicken breast pocket with the spinach filling. Pinch the edges to seal the filling inside.
5. Season Chicken: In a large oven-safe skillet, heat the olive oil over medium-high heat. Season the outside of each stuffed chicken breast with salt and pepper.
6. Sear Chicken: Add the stuffed chicken breasts to the skillet and sear for about 4-5 minutes on each side until they turn golden brown.
7. Add Breadcrumbs (Optional): If using breadcrumbs, sprinkle them on top of each chicken breast after searing for a crunchy finish.
8. Bake Chicken: Transfer the skillet to the preheated oven and bake for 25-30 minutes or until the chicken reaches an internal temperature of 165°F (74°C).
9. Rest: Once cooked, remove the chicken from the oven and let it rest for about 5 minutes to allow juices to redistribute.
10. Serve: Slice the stuffed chicken breasts in half to reveal the beautiful filling and garnish with fresh herbs if desired.

By following these organized steps, you will end up with perfectly cooked spinach stuffed chicken breasts that are not only delicious but also visually stunning.