Cook the pasta according to package instructions until al dente. Drain and set aside.
Pat chicken breasts dry and rub both sides with the Cajun seasoning. Season lightly with salt and pepper.
Cooking
Heat olive oil in a large skillet over medium heat. Add the seasoned chicken. Cook for 5–7 minutes per side, or until golden brown and the internal temperature reaches 165°F (74°C). Remove chicken from the skillet and let rest for a few minutes, then slice.
Reduce heat to low–medium. Pour the heavy cream into the same skillet and scrape any browned bits for flavor. Stir in the shredded mozzarella and ranch dressing until the cheese melts and the sauce is smooth.
Add the cooked pasta and sliced chicken to the skillet. Toss gently until the pasta and chicken are evenly coated in sauce.
Fold in diced tomatoes if using. Taste and adjust salt and pepper.
Garnish with chopped parsley and serve warm.
Notes
Store leftovers in an airtight container for up to 3–4 days. Reheat on the stovetop over low heat with a splash of milk or cream. Freezing is possible for up to 2 months.