Season the chicken breasts with salt and pepper.
Over medium-high heat in a large skillet, heat olive oil.
Add the chicken breasts and cook for about 4-5 minutes per side, until they are golden brown and cooked through. Remove them from the skillet and set aside.
Add the chopped onion and garlic in the same skillet. Sauté for 2-3 minutes until they become fragrant and translucent.
Add the sliced mushrooms and cook for another 3-4 minutes until they are tender.
Stir in the diced tomatoes, tomato sauce, dried oregano, and dried basil. To let the flavors mix well simmer for about 5 minutes.
Preheat your oven to 375°F (190°C).
Transfer the chicken breasts to a baking dish and spoon the tomato mushroom sauce over them.
Sprinkle the shredded mozzarella cheese evenly over the chicken.
Bake in the preheated oven for 15-20 minutes or until the cheese is bubbly and golden.
If you like, you can add a finishing touch of fresh basil leaves and serve hot.