Pick through the beans to remove any debris like small stones or seeds before placing them into a bowl and covering them with water to soak about 5-6 hours or overnight. Drain the beans when ready to cook.

Transfer the beans to a soup pot. Peel and cut the onion in half and place it into the pot. Fill the pot with water to just cover the beans. Put them on the stove over high heat and bring them to a boil. Reduce the heat to low and let the beans simmer for about 2 hours. Add the salt to the pot about 15 minutes before the beans are done and stir well.

Strain the cooked beans of excess water with a colander in the sink.

On a cutting board, dice the onion, tomatoes, and bell pepper. Mince the oregano. Reserve ¼ of the tomato and bell pepper for later.

Heat the olive oil in a skillet over medium-high heat. Add the onion and saute 2 minutes. Add the bell pepper, stir, and cook another 2 minutes. Add the tomato, cumin, and salt to the pan and stir well. Let this mixture cook 6-8 minutes, stirring occasionally.

Turn the heat down to medium and add the black beans to the pan, stirring well to combine. Using a fork, mash some of the beans into the rest of the ingredients. Pour in about half of the vegetable stock and stir well. Allow this to simmer 16-18 minutes, stirring occasionally.

Once the liquid has reduced significantly, add more of the stock and stir again to combine. Mash the beans into the mixture again, stir, and allow to simmer another 1Repeat this process 2 more times, using the water to add liquid to the beans in between mashing.

Turn off the heat, cut the lime in half and squeeze it over the beans. Stir well, taste and season with salt if needed.

Serve the beans with shredded cheese, the reserved bell pepper and tomato, and a slice of lime.