Bring a large pot of salted water to boil for the pasta.
While waiting for the water, prepare the pesto. In a food processor, combine basil, pine nuts, garlic, and Parmesan cheese. Pulse until coarsely chopped.
With the processor running, slowly drizzle in olive oil until the mixture is smooth. Add lemon juice, salt, and pepper to taste. Set aside.
Season the diced chicken with salt and pepper. Heat 2 tablespoons of olive oil in a large skillet over medium-high heat.
Cook the chicken pieces until golden brown and cooked through, about 6-8 minutes. Remove from heat and set aside.
Cook pasta according to package instructions until al dente. Reserve 1 cup of pasta water before draining.
Return the pasta to the pot, add the cooked chicken and pesto sauce. Toss everything together, adding pasta water as needed to create a silky sauce.
Serve hot, garnished with extra Parmesan cheese and cherry tomatoes if desired.