One Pot Cajun Chicken Pasta

Name: One-Pot Cajun Chicken Pasta
Ingredients: Kosher salt; 1 cup grated Parmesan cheese; 2 medium scallions; 2 medium tomatoes; 1/4 cup fresh parsley leaves and fine stems; 4 tablespoons unsalted butter; 1 pound dried penne pasta; Freshly ground black pepper; 1 tablespoon salt-free Cajun spice blend; 1 1/2 pounds skinless boneless chicken breasts; 2 tablespoons olive oil, plus more for the pasta