Wash potatoes then cut in chunks. Simmer in lightly salted water until tender. Drain, reserving cooking liquid. Mash potatoes with butter, enough milk to make a fairly soft consistency. After mashing, beat potatoes with a fork until light and fluffy.
Heat oil in a large pot. Add onions. Cook until tender and well browned. Add capsicum and flour. Stir until flour is lightly browned. Add remaining ingredients except kidney beans then bring to the boil, stirring constantly. Add kidney beans either whole, roughly chopped or mashed. Taste and adjust seasoning as required.
Spreads vege and bean mixture into a lightly sprayed 20x25cm baking dish. Cover with spoonfuls of mashed potato. Sprinkle grated cheese over the top. If not cooking immediately, refrigerate.
Bake uncovered at 180°C for 20-30 minutes or until top is golden brown.