Balsamic Chicken & Onions over Tortellini

We have made this before but last time we just had it over plain pasta. This time I decided to try it over spinach and cheese tortellini and it was really great! My husband loved it. I think next time I will make it with chicken thighs instead and see how it is. I have Sucanat here and I was thinking if trying that next time instead of the brown sugar but I wasn't sure it would work the same and I had brown sugar to use up anyway.

Balsamic Chicken with Onions
written by Rachel L - http://cookingformyfamily.blogspot.com/
3 chicken breasts (could use 4 I would think)
1 onion, sliced in rings
1 cup balsamic vinegar (or around there, I didn't measure)
1/4 cup brown sugar (again, just a guess)
olive oil for cooking
Heat the pan with a little olive oil on the bottom. Toss the onions in and cook them on medium heat until soft and caramelized. Take the onions out of the pan, add more oil if needed, and cook the chicken until it is all the way done (for us that was about 5-7 minutes on each side, but it will vary depending on size of the chicken). Remove the chicken. Turn the heat on the pan to low. Pour the balsamic vinegar into the pan and scrape up the little bits on the bottom of the pan (adds flavor). Add the brown sugar and let it cook on low until it thickens up a bit and the sugar is disolved into the vinegar. Add the chicken and onions back to the pan and let them soak up the juices. We served this over noodles but many things could be done with it or it would be good plain as well.