Cut the flank steak about 6 inches in length. Using a pressure cooker add the flank steak, the water, onions, the garlic and salt to taste.
Close the pressure cooker and at high heat, cook the meat until the pressure cooker starts to whistle. Reduce the heat to low and continue cooking for 25 minutes.
Drain (you can save the broth to make a delicious soup) and with the help of two forks, shred the meat in strings.
In a sauce pan at high heat, using half of the oil, cook half of the meat until it browns. Remove the cooked meat into a bowl and repeat the procedure for the other half. Once the second half is browned, remove all of meat from the sauce pan and add to the bowl.
Using the same saucepan, heat the rest of the oil on high and sauté the onions until soft. Add the meat and stir well. Add the lime and continue cooking until the onions brown as well.
Serve with white rice and black beans.