Place the halved chicken breasts on a lined baking sheet, lightly drizzle with olive oil and season with ground black pepper. Spread 4 tablespoons pesto evenly over each breast, cover with 3 to 4 Roma tomato slices, and top with the shredded mozzarella cheese.
Place rack in the center of the oven and preheat to 400 degrees. Bake chicken for 20 to 25 minutes, or until a meat thermometer reaches an internal temperature of 165 degrees, and the cheese has melted and browned.
Let meat rest for several minutes before cutting the chicken on the diagonal into pieces, if desired. Drizzle any pan juices and olive oil over the top before serving.
FOR THE PESTO:
Blend the basil, pecans, garlic, cheese and olive oil in a food processor until the mixture becomes a slightly chunky paste. Season to taste with salt and pepper then pulse to combine seasonings.
If not using immediately, store covered in the refrigerator for up to 2 days or freeze.
Chicken shown is not cooked and must be prepared according to recipe.