Set out a food processor. Place the basil leaves, pine nuts, pecorino cheese, garlic clove, and lemon juice in the food processor. Cover and pulse until finely ground.
Then add in the olive oil, ½ teaspoon salt, and ¼ teaspoon ground pepper. Pulse again until a smooth, thick pesto sauce is formed. Taste, then salt and pepper as needed.
For the Pesto Chicken Pasta:
Set a large pot of salted water over high heat, and set out a mixing bowl. Once the water is boiling, stir the pasta into the water. Cook to al dente, according to the package instructions. Drain the pasta and place in the bowl.
Stir in the shredded cooked chicken. Allow the temperature of the pasta to come down a little, as to not cook the pesto. Once the pasta is warm (not hot) stir in the pesto, one half cup at a time, until it is as saucy as you like.
Serve at room temperature, or cold. Cover and chill until ready to serve.
Pesto is best when fresh, but does still taste amazing after several days. Therefore this is a great make-ahead up to 4 days in advance.Pro Tip: Turn this classic basil pesto into a brilliant creamy pesto sauce by adding ½-1 cup of heavy creamy at the end.