Preparation

• Position a rack in the center of the oven and heat the oven to 200°F.
• In a medium bowl, combine the tomatoes, basil, 3 Tbs. of the oil, the vinegar, garlic, 1/4 tsp. salt, and 1/8 tsp. pepper.
• Butterfly each chicken breast by slicing it horizontally almost but not entirely in half so you can open it like a book. Open and pound each breast between two pieces of plastic wrap with a meat mallet or the bottom of a heavy pan until 1/4 inch thick.
• Pat the chicken dry and season lightly with salt and pepper. Heat 1 Tbs. of the remaining oil in a 12 inch skillet over medium-high heat until shimmering hot. Cook two of the breasts until golden-brown on one side, 2 to 3 minutes. Flip and continue to cook until just cooked through, about 30 seconds more. Transfer to a rimmed baking sheet and keep warm in the oven. Repeat with the remaining 1 Tbs. oil and chicken.
• Divide the arugula among 4 dinner plates. Set the chicken on top, and spoon a generous amount of the tomato mixture and its juice over all.