Preheat oven to 350°F. Cover a baking sheet with aluminim foil, and set aside.
In a medium or large bowl, mix together diced tomatoes, minced garlic, chopped basil, kosher salt, and 1 tablespoon of olive oil.
Brush the remaining two tablespoons of olive oil onto the bread slices (lightly oil both sides). Place slices on top of the prepared baking sheet, about an inch apart from each other. Be careful not to crowd the pan.
Top each slice with about one tablespoon of the tomato mixture. Bake for 10 minutes in a 350°F oven, or just until the edges get golden brown.
Drizzle a little balsamic vinegar over each slice. Sprinkle some freshly ground black pepper (if desired) and some of the remaining fresh basil over each slice. Serve immediately.
Notes
You can use more olive oil to brush the bread before baking if you wish. Be careful not to soak the bread in the olive oil; the more oil you use, the crisper your bread slices will be. Too much oil can burn the bread. Feel free to use more tomatoes if you'd like!