First boil the meat in some water and when the water is absorbed pour the oil and saute. Immediately add the onion and then the tomato and season with salt and pepper.
When the meat is half done, remove it from the pot and add the potatoes. Before the potatoes are done, return the meat to the pot (keep the meat on one side of pot and potatoes on the other). Season with salt and pepper, add 2-3 glasses of water, cover the potatoes with a plate so as not to spread and let boil for 45 more minutes.