Bring a large pot of salted water to a boil. Cook spaghetti according to package instructions until al dente. Reserve 1 cup of pasta water, then drain.

While water heats, cut chicken into 1-inch cubes and toss with 1 tablespoon of Cajun seasoning until evenly coated.

Heat olive oil and 1 tablespoon butter in a large skillet over medium-high heat. Add chicken and sear for 3-4 minutes per side until browned and cooked through. Remove chicken to a plate.

Reduce heat to medium. Add remaining 2 tablespoons butter to the skillet. Sauté minced garlic for 30 seconds until fragrant.

Pour in chicken broth to deglaze the pan, scraping up browned bits. Let reduce for 2 minutes.

Stir in heavy cream and remaining 1 tablespoon Cajun seasoning. Simmer gently for 3-5 minutes until sauce thickens slightly.

Remove from heat and whisk in parmesan cheese until smooth. If sauce is too thick, stir in a splash of reserved pasta water.

Add cooked spaghetti and chicken back into the pan. Toss to coat evenly in the sauce. Garnish with parsley and serve immediately.