Place the onions and bell peppers in a bowl and add the black pepper, garlic, oregano and bay leaves. Let marinate for 30 minutes. Preheat the oven to 350 degrees F.
Heat the oil in a large oven-proof cooking pot like a Dutch oven. When the oil is hot, add the vegetable mixture from bowl and saute until soft. Add the roast and brown on all sides for 5 minutes, or so. Add the wine and vinegar and allow to reduce briefly. Add 2 cups of the broth and all the remaining ingredients. Bring to a boil, then place in the oven for 1 hour.
Check at intervals, adding the remaining 2 cups of chicken broth, if needed. Remove the meat from the oven and let sit for 30 minutes. Strain the sauce. To serve: slice the meat about 3/4-inch thick and serve with the sauce.