Preheat oven to 350° F.
Trim any excess fat from the chicken and place between pieces of parchment paper.
Pound chicken to even thickness (approximately ½ inch) with a meat mallet.
Sprinkle both sides with salt and pepper and transfer to a baking dish. Ensure the chicken fits snugly for best cooking with not a lot of extra space in the pan.
Spread pesto sauce over the top of the chicken breasts and cook for about 20 minutes, then add the sliced tomatoes and parmesan cheese, if desired.
Continue cooking until chicken is cooked through (about 15–20 additional minutes). Add sliced olives as garnish, if desired, and serve.