Cook the 12 ounces uncooked 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 1 pound boneless skinless chicken breasts. Heat half of the 2 tablespoons olive oil, in a pan over medium-high heat.
Season the chicken on both sides with 2 teaspoons 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 ½ cup minced onion for 3-4 minutes or until softened. Add the 2 teaspoons minced garlic and 2 teaspoons anchovy paste, and cook for 30 seconds.
Reduce the heat to medium-low and add the ¼ cup capers, ½ cup kalamata olives, ¼ cup chopped fresh basil, and 2 cups 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.