15 Kalamata or black olives, pitted and finely chopped
4 anchovy fillets, finely chopped (optional)
3 tablespoons capers, drained (optional)
3 tablespoons tomato puree
1/2 teaspoon crushed red pepper flakes, or to taste
Kosher salt and freshly ground black pepper
Cook pasta according to package directions. Drain and return to pan.
Meanwhile, heat half of olive oil in large skillet over medium-high heat. When hot, add half of chicken pieces. Cook about 5 minutes, until chicken is cooked through, stirring frequently. Remove chicken from skillet. Repeat with remaining oil and chicken. Remove chicken from skillet.
Add garlic to skillet. Cook 1 to 2 minutes until golden, watching carefully so garlic does not burn. Once garlic begins to turn golden, add tomatoes. Cook 2 minutes; stir in olives, anchovies, capers, tomato puree and red pepper flakes. Cook 10 minutes, stirring occasionally.
Return chicken to skillet; heat through. Add spaghetti, toss to coat. Season with salt and pepper as desired. If sauce is too thick, add all or part of the reserved tomato liquid until sauce is desired consistency.