Preheat Oven to 375°F.

In a small bowl, stir together paprika, cayenne, onion powder, garlic powder, oregano, salt, and pepper. Set aside 1 teaspoon for the sauce later.

In a large skillet over medium-high heat, heat olive oil. Add cubed chicken and sprinkle with the seasoning mix (except the reserved teaspoon). Cook until the chicken is no longer pink and fully cooked through, about 6–8 minutes. Transfer to a bowl and set aside.

In the same skillet, melt 2 tablespoons of butter. Add minced garlic and sauté for 1–2 minutes until fragrant. Pour in chicken broth, remaining 4 tablespoons of butter, half and half, Parmesan cheese, and the reserved teaspoon of seasoning. Whisk well and let the sauce simmer for 4–5 minutes until slightly thickened. Remove from heat.

Spoon a thin layer of sauce into the bottom of a 9x13-inch baking dish to prevent sticking.

Add 1½ cups of shredded cheese to the cooked chicken and stir to combine. Spoon the chicken mixture into the cooked pasta shells and place them open-side-up in the prepared baking dish.

Pour the remaining Alfredo sauce over the shells and top with the rest of the shredded cheese. Bake for 15–20 minutes, or until the cheese is melted and bubbling at the edges.

Sprinkle with fresh parsley and red pepper flakes (if desired). Serve hot.