Heat oil in a large skillet over medium high heat. Add garlic, saute for 1 minute; then add chicken, onion, and pepper--cook for 7 to 8 minutes on each side. When chicken is close to being cooked through (no longer pink inside), add spinach and saute all together for 3 to 4 minutes.
In a large pot of salted boiling water, cook pasta for 8 to 10 minutes or until al dente. Rinse under cold water and drain.
Meanwhile, prepare Alfredo sauce according to package directions. When finished, stir in 2 tablespoons pesto
Add chicken/spinach mixture to pasta, then stir in pesto/Alfredo sauce. Mix well, top with cheese and serve.