Heat the olive oil in a large Dutch oven over medium. Add the onion, jalapeño, and garlic, and sauté for 5 minutes or until just starting to brown.
Peel the papery husks from the tomatillos. Rinse the tomatillos in warm water to remove the sticky residue that the husks leave behind. Chop the tomatillos, and add to the onion mixture. Add the oregano and cumin, stirring to combine. Cook for 6 to 7 minutes to soften the tomatillos.
Add the broth, beans, and salt; bring to a boil over medium-high. Reduce the heat to medium, and simmer 20 minutes. Add the chicken and cook until done, about 5 minutes. Serve with the cilantro, sour cream, avocado, and cheese, if desired. This yields 10½ cups of chili.