Score the surface of each chicken breast with shallow diagonal cuts.
Whisk together olive oil, soy sauce, salt, pepper, oregano, rosemary, brown sugar, and minced garlic.
Coat the chicken in the marinade, cover, and refrigerate 30 minutes.
Slice the red onion and arrange in the bottom of a baking dish.
Layer tomato slices over the onion.
Place the marinated chicken on top of the vegetables.
Bake at 356°F for 30 minutes.
Top with shredded mozzarella and bake 15 more minutes until melted and golden.
Tip: Let the chicken rest a few minutes after baking for juicier slices.