Cook the spaghetti according to the package directions until al dente. Drain the pasta and set it aside in the pot.
While the pasta cooks, prepare the chicken breasts. Heat half of the olive oil in a pan over medium-high heat.
Season the chicken on both sides with Italian seasoning and salt and pepper to taste. Place the chicken in the pan and cook for 4-5 minutes per side or until cooked through.
Set the cooked chicken aside on a plate. Add the remaining oil to the pan and cook the minced onion for 3-4 minutes or until softened.
Add the minced garlic and anchovy paste, and cook for 30 seconds.
Reduce the heat to medium-low and add the capers, kalamata olives, fresh basil, and marinara sauce, bring to a simmer and cook for 5 minutes.
Pour the sauce over the cooked pasta and stir to coat. Serve plates of pasta with the cooked chicken on top.
