Cook penne according to package instructions. Drain and set aside.

Pat chicken dry with a paper towel and dust both sides with Cajun seasoning until thoroughly coated. In a large sauté pan over medium heat, melt 1 tablespoon butter. Add chicken, cooking through completely, about 5 to 6 minutes for each side. Remove chicken from skillet and set aside.

Add remaining 2 tablespoons butter to skillet, along with half-and-half, garlic powder, salt and pepper and 1/3 cup Parmesan. Stir until combined and remove from heat.

Toss pasta in sauce and divide onto two plates (there will be some leftover). Slice chicken and place atop pasta. Sprinkle each with remaining Parmesan, diced tomatoes and parsley and serve.