Heat a pot of salted water to boiling. When ready, add spaghetti and cook until al dente (about 10 minutes).
While pasta water heats, wash and dry basil. Remove leaves from stems.
Next, prep and start chicken cutlets. Heat oil in a skillet. Salt and pepper each side of chicken cutlets. Add chicken to pan. Don't overcrowd. May need to cook in batches. Cook until internal temperature reads 165℉, 3-5 minutes per side.
While the chicken cooks, prepare the pesto. Combine basil leaves, pine nuts (or alternative) and garlic in a food processor until finely minced. With the machine running on the slowest setting, dribble in the oil and process until smooth. Add the cheese, salt and lemon juice and process briefly, just until combined.
Once pasta is ready, drain, preserving some of the pasta water. Add pesto sauce to the pasta. Toss and add a splash of the reserved pasta water. Toss until mixed.
When chicken is ready, serve sauced pasta and top with sliced chicken.