Heat 1 tablespoon of olive oil in a large skillet over medium heat. Add the diced potatoes and season with salt and pepper. Cook for about 10-12 minutes, stirring occasionally, until the potatoes are golden and tender. Once done, transfer them to a plate and set aside.
In the same skillet, add the remaining tablespoon of olive oil and increase the heat to medium-high. Add the thinly sliced beef sirloin or flank steak. Season with salt and pepper. Sauté for about 3-5 minutes or until the beef is browned and cooked through. Remove the beef from the skillet and set aside.
In the same skillet, add the sliced onion, minced garlic, and sliced jalapeño peppers. Sauté for about 3 minutes until the onions become translucent and the mixture is fragrant.
Stir in the chopped Roma tomatoes, ground cumin, and dried oregano. Cook for an additional 2-3 minutes until the tomatoes begin to break down and the mixture becomes saucy.
Return the cooked beef to the skillet along with the potatoes. Pour in the tomato sauce and mix everything together. Simmer for about 5 minutes, allowing the flavors to meld. Taste and adjust seasoning with salt and pepper as needed.
Remove the skillet from heat and garnish your Bistec Ranchero with freshly chopped cilantro. Serve hot with rice or warm tortillas for a truly authentic experience!