Sort through the beans, removing any bad beans or small stones.
Peel and chop the onions and add them to a large pot.
Rinse the beans thoroughly and add them to the pot.
Add the water to the pot, along with the salt, oregano, garlic, and black pepper, and the jalapeño pepper, if using.
Bring to a boil over medium-high heat, then reduce to a simmer and cover.
Simmer until the beans are tender, approximately two hours. Stir occasionally and add additional water if needed.
Notes
You don't need to pre-soak your beans, but if you do, your cooking time will be reduced slightly. You will also need to use less water. Add just enough water to cover by about half an inch (1.5 cm).