Drain the spinach. Place the spinach into a clean kitchen towel and twist to remove the excess water.

Make the stuffing. Add the spinach to a medium mixing bowl along with ½ cup of chopped walnuts. Add the sun dried tomatoes, parsley, garlic, ricotta, mozzarella, and parmesan. Season with the oregano and a pinch of salt and pepper. Drizzle with a little olive oil, and mix until well combined.

Prep the chicken. Pat the chicken breasts dry and season on both sides with salt and pepper. Make a pocket in each chicken breast by slicing in the thickest part.

Stuff the chicken breasts. Spoon the stuffing mixture into the pocket of each chicken breast and evenly divide the stuffing.

Sear the chicken. In a large cast iron skillet, heat 3 tablespoons olive oil over medium-high heat. Cook the chicken for 5 to 7 minutes on one side, then turn over and cook for another 5 minutes until the internal temperature reaches 165°F.

Finish and serve. Remove from heat and allow the chicken to rest for 3 to 5 minutes. Garnish with the remaining walnuts, a bit of parsley and sun dried tomatoes.