In large 5 6 quart kettle cook onions and green pepper in oil over medium-hig h heat, stirring occasionally, until onions are golden, and pepper is soft. Ad d mustard seeds and cook for one minute, stirring as it cooks. Add chili powde r, cumin, cocoa, cinnamon, tomatoes and their liquid, beans and their liquid, c arrots, mushrooms, and tomato paste. Reduce heat and simmer rapidly, uncovered for about 40 minutes, or until most o f the liquid has cooked away and chili is thickened; stir frequently to prevent scorching. Note: In place of the cooked kidney beans, you may use 3 16-ounce cans no-salt -added kidney beans plus 1 cup water.