Step 1

Fill a Dutch oven or large pot two thirds of the way with salted water and bring to a boil. Meanwhile, prepare the following ingredients: grate 1 cup Parmesan cheese, dice 2 tomatoes (about 1 cup), thinly slice the light green and white parts of 2 scallions, and coarsely chop 1/4 cup fresh parsley leaves if desired. Cut 4 tablespoons unsalted butter into 4 pieces.

Step 2

Add 1 pound dried penne pasta to the boiling water and cook until just shy of al dente (it should still be a little too tough to chew), about 8 minutes. Meanwhile, place 1 teaspoon kosher salt, 1 teaspoon freshly ground black pepper, and 1 tablespoon Cajun spice blend in a large bowl and stir to combine. Pat 1 1/2 pounds chicken breasts dry with paper towels. Cut into 1-inch pieces, add to the bowl, and toss to combine.

Step 3

When the pasta is ready, reserve 1/2 cup of the pasta water, then drain the pasta in a colander. Immediately drizzle it with a little olive oil, and toss to coat the noodles so they don’t stick together. Leave the pasta in the colander.

Step 4

Wipe out the pasta pot, then add 2 tablespoons olive oil and heat over medium-high heat until shimmering. Add the chicken, spread into an even layer, and leave untouched for 1 minute. Flip the chicken over. Repeat until the chicken is cooked through and browned in spots, about 4 minutes total.

Step 5

Add the pasta, butter, and 1/4 cup of the pasta water, and stir to combine until the butter just starts to melt, about 1 minute. Add the Parmesan a little at a time, stirring vigorously and constantly with a wooden spoon, to form a thick sauce that clings to the noodles, about 2 minutes. If it appears dry, add 1 tablespoon of the pasta water at a time until it reaches your desired consistency.

Step 6

Remove from the heat and stir in the tomatoes. Taste and season with salt and pepper as needed. Divide between plates and top with the scallions and parsley, if using.