1. Chop onions, red bell pepper, and green bell pepper into pieces about 1/2 inch square. Heat olive oil in a large frying pan, then saute onions and peppers until they begin to soften, then add to slow cooker.
2. Squeeze Italian sausage out of casings and add to frying pan, adding a bit more olive oil if needed. Brown sausage well, breaking apart with turner as it cooks, then add to slow cooker.
3. Pour beans into a colander placed in the sink and rinse with cold water until no more foam appears, then add to slow cooker. Add tomatoes with juice, dried basil, dried oregano, ground fennel, black pepper and bay leaves to slow cooker. Pour chicken stock over other ingredients and stir to combine.
4. Cook on high about 4 hours or on low for all day. Serve hot, with freshly grated parmesan cheese for sprinkling on the stew.