Add the steak and beef broth to a large pot. If it’s a large piece cut it in half so it fits in the pot without folding or overlapping.
Set the pot over high heat. When the broth comes to a boil lower the heat to medium and cook 15 minutes.
Turn the steak, lower the heat to medium-low and cook 30 minutes. Turn the steaks again about halfway through the cooking time.
Remove the pot from the heat; place the flank steak on a cutting board or a pan. When it’s cool enough to handle, shred the steak to resemble thin strings.
Add the meat back into the broth. Sprinkle with the salt, garlic powder, black pepper and lime juice. Stir well to combine.
Heat the oil in a large, skillet over medium-high heat. When the oil is hot, almost smoking, add the shredded beef and arrange it so it covers the entire skillet in one layer.
Cook the beef for 3-5 minutes, do not stir. Let the liquid cook out and allow the bottom become browned and crispy.
Using a large spatula, get under a section of the beef and flip (don’t stir). Pick another section and flip, repeat until all of the shredded beef is browned side up.
Cook the beef for another 1-2 minutes. This side will brown a lot faster since the liquid has cooked out already. Check a section after 1 minute to make sure it’s not burning.
Flip over any sections that need to brown a little more. Keep checking and flipping until the beef is golden and crispy on the outer layer.
When the vaca frita is done, remove the skillet from the heat and place the beef on a plate or pan.
Add the sliced onions to the skillet; place it back over the hot burner (with the heat off). Let the residual heat cook the onions, stir frequently.
Serve the vaca frita with the onions and extra lime wedges, white rice, black beans or your favorite side dishes.