Preheat your oven to 375 degrees Fahrenheit (190 degrees Celsius).
Slice the tomatoes and the mozzarella cheese in 1/4 inch think slices.
Pat the chicken breasts dry with paper towels and make 5-6 slits in each breast (about 1/3 inch apart from each other). The slits should be a bit diagonal (from the top side to the bottom of the breast) and go 3/4 deep in the breast.
Mix the salt, pepper, and garlic powder and rub the mix on the chicken breasts (including the slits) on both sides.
In your baking dish, add the olive oil and the chicken breasts slit side up.
Add little dollops of pesto in each slit.
Starting at the bottom add a slice of mozzarella and a slice of tomato in each slit (with the mozzarella laying on top of the tomato).
Spread the rest of your pesto on the breasts (between the slits). Add the shredded Parmesan all over.
Bake at 375 degrees Fahrenheit (190 degrees Celsius) for 25-30 minutes until the mozzarella is golden brown and the chicken is cooked through to an internal temperature of 165 degrees Fahrenheit (74 degrees Celsius).
Serve immediately.