Shred cooked chicken breasts with two forks and transfer chicken to the baking dish. Set aside. (If you need a good recipe for baked chicken, grab my recipe for perfectly baked chicken breasts)
In a mixing bowl combine the basil pesto, mayonnaise, half of the parmesan cheese, salt, and pepper; stir until well combined.
Add the pesto mixture to the chicken mixture in the baking dish and stir to mix it all together.
Arrange cherry tomatoes and mozzarella cheese over the chicken.
Sprinkle remaining parmesan cheese on top.
Bake for 20 to 22 minutes, or until golden brown on top.