Coat a ridged grill pan with cooking spray; set over medium-high heat. (Alternately, coat an outdoor grill with cooking spray; heat grill to medium-high). Sprinkle chicken with salt and pepper; grill 2-3 minutes. Flip chicken; grill until just cooked through, 1-2 minutes more. Transfer to a platter; let rest 5 minutes. While chicken rests, combine tomatoes, olives and capers in a medium bowl; set aside. Heat oil in a small skillet over medium heat; add garlic and red pepper flakes. Sauté until just fragrant, about 30 seconds. Stir in anchovy paste, if using. Add garlic mixture to tomato mixture; sprinkle with basil and stir gently. Serve chicken with sauce spooned over top. Serving size: 3 oz chicken and 1/2 c sauce