Preheat oven to 375 degrees.
Add tomatoes, basil, garlic, salt and pepper to a bowl; stir to combine, set aside.
Place bread bowl on a baking sheet. Cut the bread bowl in 1/2 inch slices, being careful not to slice all the way through the bread. Then cut 1/2 inch slices going the opposite direction (think checkerboard), again, being careful not to cut through the bread all the way. (see video above)
Stuff tomato mixture into cracks/creases of the bread, distributing as evenly as possible. Then stuff mozzarella cheese into cracks and on top of bread. Carefully cover with foil, tenting it so that it doesn't touch the top of the bread/cheese. Place into oven and bake for 10-12 minutes.
While the bread is baking, add balsamic vinegar and sugar to a small sauce pot over medium high heat. Whisk until sugar is dissolved and bring to a boil. Reduce heat to a simmer, and simmer for about 5 minutes, whisking occasionally. Remove from heat and set aside.
Remove the bread from oven and remove foil. Set oven to broil, and place back into oven and broil for 2-3 minutes or until lightly browned. Be careful not to burn the bread.
Transfer the bread to a platter and then drizzle with your balsamic glaze. Add more chopped basil as a garnish if desired. Serve immediately.
Recipe originally published Aug. 2016. Updated January 2020.