Bring a pot of water to a boil. Cook the rigatoni according to package directions until al dente, then drain and set aside.
Heat the olive oil over medium heat in a large pan. Add the seasoned chicken and cook for about 5 to 7 minutes on each side until fully cooked and golden brown. Remove the chicken from the pan and set aside.
In the same pan, add a few tablespoons of water and scrape up any browned bits from the bottom. This adds flavor! Melt the butter in the pan, then add the flour and stir until a paste forms.
Slowly add the milk while whisking continuously to avoid lumps. Cook the sauce until it begins to thicken, around five minutes.
Stir in the pesto until well combined. Turn off the heat and add a quarter cup of Parmesan cheese, stirring until melted and smooth.
Add the cooked rigatoni to the creamy sauce and stir to coat thoroughly.
Slice the cooked chicken into bite-sized pieces and fold into the pasta mixture, ensuring everything is nicely mixed.
Top with the remaining Parmesan cheese and place the pan under the broiler for a few minutes until the cheese is melted and bubbly.
