Heat 1 tablespoon olive oil in a large pot over medium-high heat.
Toss chicken with 1/2 tablespoon Cajun seasoning. Add to pot in a single layer and cook until browned and cooked through. Remove and keep warm.
Add remaining olive oil to the pot. Sauté bell peppers and onion for 3 minutes.
Add garlic and remaining Cajun seasoning; sauté 1 minute until fragrant.
Pour in chicken broth, diced tomatoes, and 1/2 cup heavy cream. Bring to a boil.
Add pasta and cook, stirring often, until nearly tender (12–13 minutes).
Stir in cornstarch slurry and cook 1 minute until sauce thickens.
Remove from heat. Stir in remaining cream, parmesan, parsley, and cooked chicken.
Season with salt and pepper and serve warm.