In a gallon size Ziploc bag, add the chicken breast, 1 tablespoon of olive oil, and the cajun seasoning. Shake to coat thoroughly.
Heat the remaining 1 tablespoon of olive oil in a grill pan over medium-high heat. Add the chicken and cook, flipping once, until cooked through, which will take about 5-6 minutes on each side. Slice into strips or cubes, and set it aside.
In a large pot of boiling salted water, cook the penne pasta according to package instructions and drain well. Set aside.
Next, melt the butter in a saucepan over medium heat. Add the garlic, and cook until fragrant- about 2 minutes. Be sure to stir frequently to avoid burning.
Gradually whisk in the heavy cream and lemon zest. Cook, whisking continually until the ingredients are well-incorporated, about 1-2 minutes. Then stir in the Parmesan until slightly thickened, about 1-2 minutes. If the mixture is too thick, add a bit more heavy cream as needed; season with salt and pepper, to taste.
Stir in the pasta and gently toss to combine.
Add the sliced chicken on top of the pasta, and garnish with parsley if desired.
