Saute onion, bell peppers, garlic, and mushrooms (if using) until golden brown.
In a medium size bowl, combine ketchup, chicken broth, Worcestershire sauce, and pepper.
Pour the ketchup mixture over the sauteed vegetables in the skillet.
Bring the mixture to a boil, and then pour over chicken.
Place dish in the oven and bake 1 1/2 hours (this time is based on a whole cut up chicken; you will have to adjust time if using boneless chicken breasts, or thighs.