Preheat oven to 425°F with a rack positioned in the center. Allow oven to fully preheat before baking.

In a mixing bowl, use a fork to mash together the cold cream cheese, mayonnaise, and pressed garlic until smooth. Stir in shredded mozzarella, parmesan, and chopped spinach until fully combined. Set aside.

Lay each chicken breast flat on a cutting board. Cut a slit 3/4 of the way into the breast without cutting all the way through. Stuff each breast with one-third of the filling and seal the opening horizontally with a toothpick. Ensure the chicken can lay flat for even searing.

Season the outside of each stuffed chicken breast generously on all sides with salt, pepper, garlic powder, and paprika.

Heat olive oil in a large oven-safe skillet over medium heat. Add chicken and sear for 4 minutes per side without moving until deep golden brown.

Flip one final time and immediately transfer the skillet to the preheated oven. Bake at 425°F for 10 to 15 minutes until a meat thermometer inserted into the thickest part reads 165°F. Thicker breasts will need the full 15 minutes.

Remove from oven and rest chicken for 5 minutes before slicing. Spoon pan juices over the top before serving.