Balsamic chicken sandwich (with hidden veggies)

OK, I have to say that I'm totally loving this double delicious book I have checked out from the library.  I may have to purchase this one.  It's definitely on my wishlist now.  I have to say, I was reading reviews and saw a bad one for this sandwich.  I do have to agree with the person that posted it, this sandwich ended up with a lot of liquid.  I would probably add a bit less beef broth next time, but only a little.  I added a lot of the sauce to the sandwich because the crusty bolillos we got could easily absorb a bit of liquid.  I also caught a child wiping the extra liquid off of his plate with his finger and licking it.  I'm not complaining because that is where the hidden veggies were.
I do have to agree with many of the commenters at amazon, you aren't getting a ton of veggies in there, but I'm super happy that my super picky, non vegetable eating 3 year old has eaten all 4 of the things I've made from this book.  He ate a whole 1/2 of this sandwich which is truely saying something for him.  He is super picky - has texture issues, color issues.....
I did of course have a couple of changes, but not many - just used barley flour instead of wheat, and I actually used a bit more than called for in the original. Here is what I did

Ingredients

• 2 lbs boneless, skinless chicken breast, cubed (I used 3 larger sized chicken breasts - not sure of the weight) 
• salt and pepper
• 1/3 cup barley flour (can use wheat or white as well, I just wanted to try barley)
• 2 Tablespoons oil (can't remember if I used healthy blend or coconut this day)
• 1/2 teaspoon garlic minces (been really lazy with garlic lately)
• 1 cup chicken stock (this will make a lot of sauce.  I might reduce this to about 3/4 cup next time -or just have lots of sauce.  I'm undecided at this point)
• 1/2 cup balsamic vinegar
• 6 Tablespoons dark brown sugar (mine was a brick so I guessed.)  
• 1/2 cup steamed and pureed broccoli (I made this earlier in the day -during nap time)
• 1-2 Tomatoes sliced (depending on the size of your tomato)
• 6-7 Bolillos or other type of crusty roll 
• Mozzarella cheese

Directions

1. Sprinkle chicken with salt and pepper.  Toss chicken with flour to coat (either in a ziplock bag, or on a piece of wax or aluminum foil - or in a bowl.)  
2. Warm oil in a large skillet over medium high heat.  Add chicken.  Cook until chicken begins to brown adding garlic in the last minute or 2.  
3. Add the stock, vinegar and brown sugar.  Bring to a boil.  Cover and simmer 10-15 minutes or until chicken is cooked through.  (If I didn't add less stock next time, I would boil this uncovered to reduce the sauce a bit.)  While this is simmering, preheat the oven to 350 and cut the buns in half.  (I found that I liked not cutting all the way through the bun because it caught all of the juices better and held together better in the oven -   think cut it like a hot dog bun.)
4. Add puree and cook 2-3 minutes more (I simmered it a bit longer to reduce the sauce some this time since I had left the pot covered in the previous step.)
5. Place the bread on a cookie sheet.  Top each with tomato and chicken.  Sprinkle with cheese.  Bake until the 3-4 minutes until the cheese begins to melt.  Change oven to broil and broil for 45 seconds to a minute - just until the edges begin to brown.  Serve.