Heat the oven to 375°F and grease a 3-quart baking dish.
Toss the uncooked ravioli, chicken, pesto, tomatoes, salt and pepper in the dish until the pesto coats every piece.
Cover the dish tightly with foil and bake for 20 minutes.
Remove the foil, stir the hot mixture once and scatter the mozzarella evenly over the top.
Bake uncovered for 10 to 15 minutes, until the ravioli is tender, the center reaches 165°F and the cheese browns in small spots.
Rest for 5 minutes before spooning the ravioli into shallow bowls.