In a large Ziploc bag add chicken, 1 tablespoon olive oil and cajun seasoning. Rub and shake to coat chicken. Let it sit for at least 5 minutes OR it can marinate in your fridge for up to 8 hours.
Heat remaining 1 tablespoon olive oil in a large skillet over medium high heat. Add chicken and cook about 6 minutes on each side or until heated through. Internal temperature should reach 165 degrees F. Remove to a plate and cover with foil to keep warm.
In a large pot of boiling salted water, cook penne pasta according to package instructions; drain well.
Wipe skillet clean (be careful it will be hot!) and melt butter over medium heat. Add garlic, and cook, stirring frequently, until fragrant.
Gradually whisk in heavy cream. Cook, whisking constantly, until incorporated, about 1-2 minutes. Stir in Parmesan until slightly thickened. If the mixture is too thick, add more heavy cream as needed; season with salt and pepper, to taste.
Stir in pasta and gently toss to combine.Serve immediately with chicken, garnished with tomatoes and parsley, if desired.