Heat the oil in a large pot over medium heat. Once hot (make sure it is fully preheated) add the onion and mushrooms. Cook for about ten minutes, stirring just once or twice, until all of the liquid from the mushrooms has evaporated and the mushrooms are lightly browned.
Bring the chili to a low boil, then reduce the heat to simmer, covered, for 30 minutes. Once finished cooking, taste the chili and season to your preference.
Serve hot topped with anything you'd like. Leftovers can be refrigerated in a sealed container for up to five days or frozen up to three months.
Notes
* A 400 gram (13.5 oz.) can of beans is equal to about 280 grams cooked beans.If preferred, you can use a pre-made chili powder in place of the spices listed. Be sure to use chili powder for chili (chilli), and not hot pepper flakes or hot pepper powder - check the ingredient list and make sure it has several spices listed.