Warm the oil in a large Dutch oven or other heavy pot set over medium heat. Add the onion and garlic and cook, stirring occasionally, until just beginning to soften, about 3 minutes. Stir in the Xawaash, tomato paste, and salt and cook until aromatic, about 1 minute. Stir in the water and increase the heat to high. Bring to a boil, reduce the heat to low, then stir in the beef and potatoes. Partially cover the pot (leave the lid slightly ajar so steam can escape) and simmer until the beef and potatoes are just cooked through, about 45 minutes. Stir in the carrots and bell pepper and cook, covered, until the beef and vegetables are all very tender, an additional 30 minutes. Season the stew to taste with salt and serve over rice with hot sauce and cilantro for topping, lime wedges for squeezing over, and bananas for eating alongside. Leftovers can be stored in an airtight container in the refrigerator for up to a few days and rewarmed in a heavy pot set over low heat (stir while you heat).