Preheat the oven. Set it to 400°F (200°C). Lightly oil a 9x13-inch baking dish or line it with parchment for easy cleanup.
Prep the chicken. Pat the chicken dry with paper towels. Season both sides with salt, pepper, and Italian seasoning.
If the breasts are very thick, slice them horizontally to make cutlets for more even cooking.
Add tomatoes. Toss the halved tomatoes with a drizzle of olive oil, a pinch of salt, and the minced garlic. Scatter them around the chicken in the baking dish.
Spread the pesto. Spoon about 2 tablespoons of pesto over each chicken piece. Use the back of the spoon to spread it evenly.
Don’t worry if some drips onto the tomatoes—that’s extra flavor.
Bake the chicken. Place the dish on the center rack and bake for 15–20 minutes, depending on thickness. You’re aiming for the chicken to be almost cooked through.
Add mozzarella. Remove the dish from the oven. Top each breast with generous slices or handfuls of mozzarella.
Add a pinch of red pepper flakes if you like a hint of heat.
Finish baking. Return to the oven for 8–10 minutes, until the cheese is melted and lightly browned in spots and the chicken reaches an internal temperature of 165°F (74°C).
Rest and garnish. Let the chicken rest for 5 minutes. Spoon the pan juices over the top, scatter fresh basil, and drizzle a little balsamic glaze if you want a sweet-tangy finish.
Serve. Plate with the roasted tomatoes and any extra pesto on the side. Great with a simple salad, roasted potatoes, or pasta.