Pat chicken dry, season with salt, pepper, and Italian seasoning.
Heat 1 tbsp oil and butter in a skillet over medium-high. Brown chicken 4–5 minutes per side until nearly cooked; remove and rest.
Add remaining oil and garlic; toss in bread cubes and toast until crisp, stirring, 3–4 minutes. Season croutons and remove.
Add tomatoes to skillet, cook 2 minutes until soft, then nestle chicken back in. Top with mozzarella and cover until cheese melts, about 2 minutes.
Scatter croutons and basil, drizzle balsamic if using, and serve straight from the skillet.