1. Preheat oven to 400°F (200°C).
2. Pat boneless skinless chicken breasts dry with paper towels. Lay each chicken breast on a cutting board and use a sharp knife to make a pocket by making a long vertical cut in the middle of the chicken breast without cutting all the way through. To expand the pocket, make cuts to the right and left, gently tilting your knife to create a larger space inside each chicken breast. Repeat for all the chicken breasts. Season each chicken breast with paprika, salt, and black pepper on both sides, ensuring to season inside the pockets.

3. Crumple a piece of parchment paper for each chicken breast and place inside each chicken breast's pocket.

4. Heat oil in a large skillet over medium-high heat. Once hot, add the chicken breasts to the skillet, pocket side down.

Give the chicken a quick sear for a few minutes on each side until they turn golden brown.

5. Transfer chicken to a parchment paper lined baking sheet (or a baking dish). Remove the parchment paper from the pockets of each chicken breast. Fill each pocket with 1 Tablespoon of marinara sauce, 1 1/2 Tablespoons of shredded mozzarella cheese, and 1 Tablespoon of diced pancetta.

6. Bake the stuffed breasts in the preheated oven for about 10 minutes, or until the internal temperature of the chicken (thickest part) reaches 165°F (74°C), as measured by a meat thermometer, and the cheese is melted and bubbly. Once done, remove the chicken from the oven and allow it to rest for a few minutes. 

8. Top with basil leaves. Serve your delicious chicken breasts stuffed with cheese, marinara, and pancetta. Enjoy!