Preheat the oven on broiler setting. Arrange the artisan bread slices in a single layer on a baking sheet.
Combine the roma tomatoes, sun-dried tomatoes, garlic, olive oil, vinegar, basil, salt, and pepper in a large bowl. Allow the mixture to sit for 10 minutes.
Broil the bread until slightly brown, about 1 to 2 minutes.
Divide the tomato mixture evenly over the bread slices. Top the slices with mozzarella cheese.
Return the baking sheet to the oven and broil until the cheese is melted, about 1 to 2 minutes.
