First, pre-heat the oven to 350°. Wash the grape tomatoes, and slice in half. Then set aside.
Pound the chicken out between two sheets of plastic wrap. This will even out the thickness of the chicken, allowing it to cook more evenly. Place the chicken breasts into a gallon-sized ziplock bag. Pour the marinade in the bag, and allow the chicken to marinate for at least 30 minutes before cooking.
Heat a skillet to medium-high heat. Add a couple of tablespoons of olive oil, and cook the chicken for 7 to 8 minutes on each side, or until the chicken is almost done (it will continue to cook in the oven). Remove the chicken from the skillet and place it in a baking dish.
While the chicken is cooking in the skillet, add the butter, minced garlic, and lemon juice in a small pot, and heat thoroughly.
Now that the chicken is in the baking dish, brush each piece with the butter lemon garlic sauce. Lay a slice of mozzarella cheese over the chicken, and then add a tablespoon of pesto on top. Pour the diced grape tomatoes around the chicken, and place the dish in the oven. Allow it to bake until the cheese melts, which should take about 7-10 minutes.