Place the flank steak in a large pot, cover with water, add a pinch of salt, and bring to a boil; reduce heat and simmer for about 60-75 minutes until the beef is very tender.

Remove the beef from the pot, let it cool slightly, and shred it into fine strands using two forks or your fingers; set aside.

In a large skillet, heat the vegetable oil over medium heat and sauté the chopped onion, red bell pepper, and garlic until soft and fragrant, about 5 minutes.

Add the shredded beef, tomato sauce, beef broth, cumin, salt, and pepper to the skillet, stirring well to combine.

Simmer the beef mixture on low heat for 15-20 minutes until the liquid reduces and the sauce thickens around the meat; keep warm.

While the beef simmers, combine the warm water and 1 teaspoon of salt in a large bowl, then gradually mix in the cornmeal using your hands until a smooth, non-sticky dough forms.

Let the dough rest for 5 minutes, then divide it into 4 equal portions and shape them into discs about 1/2 inch thick.

Heat a lightly oiled griddle or non-stick pan over medium heat and cook the arepas for 5-7 minutes per side until a crust forms and they sound hollow when tapped.

Slice each arepa open horizontally (leaving the back edge attached), spread a little butter inside if desired, and stuff generously with the hot shredded beef and shredded Gouda cheese.

Serve immediately while the arepas are hot and the cheese begins to melt into the savory beef filling.