In a pot, place the flank steak, water, salt and pepper. Cook over medium heat for about 1 hour and 15 minutes or until the meat is cooked.
Mean while to make the hogao: Heat the oil in a saucepan, add the tomatoes, scallions, garlic, ground cumin and cook gently for 10 minutes, stirring until softened.
Reduce the heat to low, add the salt and , cook for 10 minutes more, stirring occasionally until the sauce has thickened. Check and adjust the seasoning.
Measure 1 cup of the liquid used to cook the meat. Set aside.
Remove the beef from the pot, let it cool and shred with a fork or your hands.
In a saucepan, place the shredded beef, hogao, tomato paste and 1 cup of beef liquid. Cook for 6 to 8 minutes, stirring occasionally.
Serve hot over white rice or arepa.