In a 6-quart pressure cooker over medium-high heat, pour in 3 tablespoons oil. Add the ham hock and onions and cook until the onions are wilted and the ham hock is lightly browned, about 5 minutes. Throw in the garlic and bay leaf and cook for 1 minute more. Add the beans and give a good stir. Pour in the water; add the remaining tablespoon of oil, 1 tablespoon of salt, and a couple of grindings of pepper. Following the manufacturer's instructions, cover, lock the lid, and bring to high pressure. Lower heat to maintain pressure and start timing. Cook at high pressure for 25 minutes. Remove from heat and let rest for 5 minutes. Release the steam, again following the manufacturer's directions. If the beans are underdone, simmer them with the lid off until tender. Remove bay leaf and discard. Pick meat from ham hock and add to beans; discard the bone. Taste and adjust seasoning.
Cook's note: The oil prevents the beans from foaming and clogging the steam vent of the pressure cooker.