If using a large piece of meat, cut it into halves, thirds, or quarters so it fits in the pot without folding or overlapping.
Arrange the meat in the pot.
Add enough beef broth to cover the steaks completely.
Set the pot over high heat. Once the broth comes to a boil, lower the heat to medium to medium-low, cover, and simmer for 45 minutes.
Turn the steak and cook for another 45 minutes, keeping the broth at a gentle simmer. Adjust the heat as needed to prevent it from boiling too vigorously.
Remove the pot from the heat and transfer the flank steak to a cutting board or pan. Save the broth.
Once cool enough to handle, shred the steak into thin strands using two forks.
Return the shredded steak to the pot with the reserved broth. Sprinkle with salt, garlic powder, black pepper, and lime juice. Stir well to combine and let sit for 15 minutes.
Heat the oil in a large skillet or sauté pan over medium-high heat.
When the oil is hot, use tongs to transfer the shredded beef from the pot to the skillet, avoiding excess liquid. Arrange it in an even layer.
Cook for 3–5 minutes without stirring to allow the liquid to cook off and the bottom to develop a crispy, golden-brown crust.
Using a large spatula, flip sections of the beef (do not stir). Repeat until all of the shredded beef is browned side up.
Cook for another 1–2 minutes, keeping an eye on it, as this side will brown more quickly. Check after 1 minute to ensure it’s not burning. Flip over any sections that need more browning.
Remove the skillet from the heat and transfer the beef to a plate or pan.
Add the sliced onions to the skillet and return it to medium-low heat. Add 2–3 tablespoons of the reserved broth and cook, stirring frequently, until the onions reach your desired tenderness.
Serve the vaca frita with the sautéed onions. Garnish with fresh chopped parsley and enjoy with white rice, fried sweet plantains, or your favorite sides.