Preheat your oven to 375℉. Slice tomatoes into ½-inch slices, then set them aside.
Using the flat side of a meat mallet, pound each chicken breast to a uniform thickness. Pat the chicken dry with a paper towel, and lightly season with salt and pepper.
Drizzle oil on the bottom of the baking dish.
Lay the chicken breasts inside the baking dish. Note: It's okay if they're squished and overlapping a little, as they'll shrink while they cook. Just avoid stacking them in a large pile.
Spoon the pesto evenly over the breasts. Arrange the sliced tomatoes over the pesto.
Bake in preheated oven for 25 minutes or when internal temperature at the thickest portion of the poultry reaches 163℉. Remove from the oven, and allow the dish to rest for 5 minutes. The chicken will continue cooking to a safe internal temperature of 165℉.
Plate and garnish with fresh basil leaves and additional black pepper if desired.
Video
Notes
This dish can be prepared the night before you plan to cook it. Layer the chicken, pesto, and tomatoes in the baking dish, then cover tightly with foil or plastic wrap. Set it in the refrigerator until you're ready to cook it.
*Nutrition information does not include optional mozzarella cheese.