Cook pasta according to package directions until al dente in a large pot of salted water. Before draining, reserve 1 cup of pasta water.

While pasta cooks, heat olive oil in a large skillet over medium-high heat. Season chicken pieces with 1 tbsp of Cajun seasoning. Cook until golden and cooked through, about 5-7 minutes. Remove and set aside. Add sliced sausage to the same skillet and cook until browned. Set aside with the chicken.

In the same skillet, melt butter over medium heat. Add minced garlic and cook for 30 seconds. Whisk in flour and cook for 1 minute, stirring constantly.

Gradually whisk in the milk and heavy cream until smooth. Bring to a simmer until thickened. Reduce heat to low. Stir in the softened cream cheese until melted. Add shredded cheddar and Gruyère in batches, stirring until smooth. Stir in chicken broth and the remaining 1 tbsp of Cajun seasoning. Season with salt and pepper to taste.

Add the drained pasta, cooked chicken, and sausage to the cheese sauce. Stir to combine until everything is well-coated. Serve immediately.