Preheat the oven to 350℉.
Cut tomatoes into bite-sized pieces, and place them in a large bowl.
Add salt, pepper, garlic, onion slices, vinegar, 4 Tablespoons of olive oil, basil, and parsley. Toss them together and set aside to marinate.
On a large, rimmed sheet tray, place bread cubes, add the additional 2 Tablespoons of olive oil, then toss with your hands until well coated
Bake for 15 minutes. Remove from the oven, add butter to the pan, and toss with the bread cubes. Sprinkle with Parmesan cheese. Set aside to cool for a few minutes.
Stir tomato mixture to blend ingredients. Then add bread cubes to the bowl with the marinated tomatoes and toss until well coated. Top with shaved Parmesan, if desired.