This is a modification of a recipe I saw on Cooks.com:
4 skinless, boneless chicken breasts
1 lb mushrooms, sliced
6 cloves garlic, minced
4 T balsamic vinegar
3/4 C chicken broth
1 bay leaf
1/4 tsp dried thyme
salt and fresh ground pepper to taste
Put chicken in Crockpot; scatter the mushrooms over the top. Combine the vinegar, broth, and seasonings and pour over all. Cover and cook for 4-5 hours on High or 6-8 hours on Low. If you're using frozen chicken it will take a bit longer.
NOTE: Before serving, you may want to thicken the juices with a bit of cornstarch dissolved in white wine or broth, which will give you something nice to pour over gluten free noodles or rice.