Combine all ingredients for the sauce and set aside.
Melt the butter in a shallow frying pan. Add the red onion and red bell pepper and sauté until starting to soften. Add the garlic and sauté for one more minute.
Pour sauce ingredients into the frying pan and stir. Slide the chicken breast into the sauce and bring mixture to a heavy simmer. Cover and simmer until the chicken is cooked; about 15 minutes.
Once the chicken is done pull from the sauce and allow to cool slightly. Allow the sauce to continue to simmer, cooking down and thickening until it resembles BBQ sauce. This will take another 10-15 minutes.
Pull or slice the chicken into small pieces. When the sauce is nearly cooked down put the chicken back in the sauce and heat through.