Preheat oven to 375°F. Spray a 9x13 baking dish with non-stick cooking spray. Set aside.

Using a sharp paring knife, trim any fatty pieces off of each of the chicken breasts. Lay the trimmed chicken breast flat onto a cutting board and carefully cut a slit through the center of the chicken breast, being careful not to cut all the way through. You want to create a pocket for the filling to be stuffed into. Set aside.

To a small bowl add the olive oil, salt, black pepper, smoked paprika, garlic powder and onion powder. Stir to combine. Set aside.

In a medium skillet, on medium-high heat, add 1 tablespoon olive oil, diced yellow onion and minced garlic. Cook for 1 minute to soften the diced onion before adding the fresh baby spinach to the skillet. Cook the vegetables for 2-3 minutes or until all the spinach has wilted and the onions are translucent. Remove from the heat and allow the spinach to cool slightly before adding it to the cheese mixture.

To a large mixing bowl add the cream cheese, shredded mozzarella, grated parmesan cheese and cooled sautéed spinach mixture. Using a wooden spoon, or rubber spatula, stir to combine until the ingredients are evenly distributed.

Using a spoon, fill one of the chicken breasts with a quarter of the spinach filling mixture. Place the stuffed chicken breast into the prepared 9x13 baking dish. Repeat until all four of the chicken breasts have been stuffed and placed into the baking dish.

Using a pastry brush, brush the tops of each of the stuffed chicken breasts with the olive oil spice mixture being sure to completely cover the tops of each of the stuffed chicken breasts.

Bake the spinach stuffed chicken breasts for 35-40 minutes or until the internal temperature of the chicken reaches 165°F and the top of the chicken is lightly golden brown and the spinach and cheese filling is bubbly.

Remove the spinach stuffed chicken from the oven and allow it to rest on the counter for 5-10 minutes to allow the cheese mixture to set and cool slightly before plating and serving.