Balsamic Chicken Sandwich

2 lbs boneless,skinless chicken breasts, cubed
1/2 teaspoon salt
1/2 teaspoon pepper
1/4 cup whole-wheat flour
3 tablespoons olive oil
3 cloves garlic, minced
1 cup low-fat reduced sodium chicken broth
1/2 cup balsamic vinegar
6 tablespoons firmly packed dark brown sugar
1/2 cup broccoli puree
6 large slices tomato
6 ciabatta rolls, or 6 large slices crusty Italian bread
1/2 cup grated part-skim mozzarella

1. Sprinkle the chicken with salt and pepper.  Place the flour on a sheet of waved paper.  Toss the chicken chunks in the flour and coat completely.  Preheat the over to 350F.

2. Warm the oil in a large skillet over medium-high heat.  Add the chicken and garlic.  Decrease the heat to medium and continue to cook until the chicken begins to brown and the garlic becomes fragrant, 8 to 10 mintues. 

3. Add the broth, vinegar, and brown sugar.  Bring to a boil.  Cover and simmer 10 to 15 mintues, until the chicken is cooked through and no longer pink in the center.  Add the puree and cook 2 to 3 minutes more, until the flavors are well blended.

4. Place the bread on a large baking sheet.  Top each with a tomato slice.  Divide the chicken between the 6 pieces of bread and top with mozzarella.  Bake until the cheese is melted and edges of the bread are crisp, 5 to 7 minutes.