Slice the boneless, skinless chicken breasts into bite-sized pieces. Combine chicken with Cajun seasoning and smoked paprika in a mixing bowl and let rest for 10 minutes.

In a large pot, bring salted water to a boil and add the spaghetti. Cook until al dente, about 9-11 minutes. Drain and set aside.

In a large skillet, heat olive oil over medium-high heat. Add the seasoned chicken and cook for 6-8 minutes until browned and cooked through. Remove chicken from the skillet.

Lower heat to medium, add butter to the skillet. Once melted, sauté garlic for 1 minute, then whisk in flour to create a roux. Cook for an additional minute until bubbly.

Gradually whisk in the whole milk and chicken broth to the roux, bringing to a simmer and cooking for 3-4 minutes until slightly thickened.

Stir in cream cheese, then add shredded mozzarella and grated Parmesan cheese until melted and blended.

Toss cooked spaghetti and seared chicken into the cheese sauce, ensuring everything is well-coated.

Transfer to an oven-safe dish, sprinkle remaining mozzarella cheese on top, and broil for 2-3 minutes until bubbly and golden brown.