Cook penne pasta according to directions on the box. Drain pasta and set aside.
Place chicken breasts in a resealable plastic bag and sprinkle in cajun seasoning. Reseal bag and shake thoroughly until chicken is evenly coated.
In a large skillet, saute chicken breasts over medium heat in 2 Tablespoons of butter, turning occasionally until cooked through.
While the chicken is cooking, in another skillet whisk together 1 tablespoon of flour with 2 tablespoons of butter over medium heat to create a roux.
After the butter and flour have mixed together, combine the half and half, lemon pepper, salt, pepper, and garlic powder and continue cooking it over medium heat, stirring it occasionally.
Remove from heat when cream mixture starts to bubble.
Pour cream sauce over cooked noodles. Slice chicken breasts into strips.
Serve pasta on serving plates.
Top with chicken breast strips, and sprinkle on diced tomatoes and Parmesan cheese.