(Pressure Cooker Instructions) In the pressure cooker, combine the beans, 7 cups of water, onion, garlic, bay leaf, and salt. Cover and cook on high pressure for 25 minutes. Allow natural pressure release for at least 20 minutes, and then manually release the pressure. Discard onion, garlic, and bay leaf.
(Stovetop Instructions) Place the beans in a large pot and cover with 1 1/2 inches of water. Add the onion, garlic, bay leaf, and salt. Bring to a boil and boil for 10 minutes. Reduce heat to low and simmer until beans are soft and tender, about 2 1/2 hours. Add additional water if necessary to keep the beans covered. Remove from heat and discard onion, garlic, and bay leaf.
While the beans are cooking, roast the sweet potatoes. Preheat oven to 400. Toss the sweet potato cubes lightly with olive oil and season with salt. Arrange potatoes on a rimmed baking sheet, being sure to leave space between each piece. Roast for 25-30 minutes until edges start to turn golden brown.
To serve, ladle a portion of the black beans over the rice. Top with sweet potatoes, avocado, sliced onion, and cilantro. Generously drizzle with herbed tahini dressing and serve immediately.