Cook the pasta: Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package instructions until al dente. Drain and set aside.
Sauté the chicken: In a large skillet, heat the olive oil over medium heat. Season the chicken breasts with salt and pepper. Add the chicken to the skillet and cook for 6-7 minutes on each side until golden brown and cooked through. Remove from the skillet and let rest for a few minutes. Then, slice into strips.
Prepare the sauce: In the same skillet, add the diced onion, garlic, and bell pepper. Sauté for about 5 minutes until vegetables are softened.
Combine ingredients: Stir in the diced tomatoes with green chilies, tomato paste, Cajun seasoning, smoked paprika, and cayenne pepper. Mix well and cook for another 3 minutes.
Add broth: Pour in the chicken broth and bring the mixture to a simmer. Allow it to cook for about 5 minutes, letting the flavors meld together.
Combine spaghetti and chicken: Add the cooked spaghetti and sliced chicken to the skillet. Toss everything together, ensuring the pasta is well coated in the sauce. Cook for an additional 2-3 minutes to heat through.
Cheesy finish: Remove from heat and stir in half of the shredded cheddar cheese until melted. Top with the remaining cheese and let it sit covered for a couple of minutes until cheese is melted.
Serve and garnish: Plate the chicken spaghetti, and garnish with sliced green onions for an extra burst of flavor and color.
Notes
Adjust the cayenne pepper to taste for desired spiciness.