Prepare an outdoor grill with a hot fire.
Toss the tomatoes, garlic, scallion, the 3 tablespoons olive oil, vinegar, the 2 teaspoons salt, and black pepper to taste in a medium bowl. Add all the herbs to the bowl but don't toss.
Brush the chicken paillards lightly with olive oil and season with salt and black pepper to taste. Grill the chicken, turning once, until cooked through, about 2 minutes per side. Stir the herbs into the tomatoes. Put a paillard on each of 4 plates, spoon some herb-tomato salad on top (watch out for the smashed garlic-you might want to remove it), and serve.
Paillards, a.k.a. scaloppini, are very thin pieces of meat or fish. They cook in a wink and are easy to make: Start with a boneless, skinless chicken breast. Place between two sheets of plastic wrap or waxed paper. Use a meat pounder or the bottom of a small, heavy skillet to pound to an even thickness of about 1/2 inch. You also can save yourself time by asking your butcher to do it for you.
From Food Network Kitchens Get Grilling, Meredith, 2005