Preheat your oven to 375 degrees f.
Heat oil in a skillet over medium-high heat, add in chicken and season with sea salt and freshly ground black pepper.
Cook, stirring occasionally, until golden brown on the sides and almost cooked through.
Transfer the chicken to a 8x8 baking dish (sprayed or brushed with oil to prevent sticking), top with chopped tomatoes, oregano, garlic and a drizzle of balsamic vinegar.
Sprinkle with mozzarella cheese.
Place your casserole into the preheated oven, uncovered, and bake for 18-20 minutes, just until cheese is melty and sauce is bubbling at the bottom of the dish.
Remove from the oven, cover, and allow casserole to rest for 5 minutes, then garnish with fresh basil and enjoy!