Cosi Tomato, Basil and Mozzarella Flatbread Sandwiches

Found this one while searching for other recipes. Sandwiches seem so simple but really, how often have you thought of something different besides meat and cheese??

4 pieces Flatbread, thin Focaccia or other Bread of choice
2 tablespoons Extra-Virgin Olive Oil for brushing
Kosher Salt
3 tablespoons Balsamic Vinegar
3 teaspoons Dijon Mustard
1/4 teaspoon dried Basil
Pinch Sugar
Kosher Salt and freshly ground Black Pepper
1/2 cup Extra-Virgin Olive Oil
4 medium Tomatoes sliced (about 1 1/4 pounds)
1 1/2 pounds fresh Mozzarella sliced
16 to 20 fresh Basil Leaves
Kosher Salt and freshly ground Pepper

Dressing
Whisk the vinegar, mustard and dried basil in a bowl.
Add the sugar and 1/4 teaspoon each salt and pepper.
Slowly whisk in the olive oil.

Prepare the Flatbread
Slice each flatbread in half horizontally.
Brush top with butter, to taste, and sprinkle with salt, to taste.
Brush both inside sides of the flatbread with the dressing.

Assemble the Sandwiches
Top bread bottoms with the tomatoes, mozzarella and basil leaves. Season with salt and pepper, to taste, and cover with the bread tops.
Cut into pieces.