In a large pot or rice cooker, bring 2 cups of water minus 2 tablespoons to a boil. Add 1 cup of long-grain rice, stir, and cover. Reduce the heat to low and let it simmer for about 18-20 minutes or until the rice is tender and water is absorbed. Remove from heat and keep covered.
While the rice is cooking, peel and slice the russet potatoes into thin fries. Heat 3 tablespoons of avocado oil in a large skillet over medium heat. Add the potato slices and fry until golden brown and crispy, about 5-7 minutes. Remove from the skillet and place on paper towels to drain excess oil. Season with salt to taste.
In the same skillet, add another 2 tablespoons of avocado oil. Heat over high heat until shimmering. Cut the beef tenderloin into strips and season with salt and pepper. Add the beef to the skillet in batches, searing for about 2-3 minutes until browned but not fully cooked through. Remove the beef and set aside.
In the same skillet, add the red onion, yellow bell pepper, and jalapeño. Sauté for about 3-4 minutes until the vegetables are tender but still vibrant. Add the minced garlic and cook for an additional 30 seconds until fragrant.
Return the beef to the skillet with the sautéed vegetables. Add the soy sauce, oyster sauce, distilled white vinegar, ground cumin (if using), and beef stock. Stir well to combine and let it cook for another 2-3 minutes until the beef is cooked through. Gently fold in the Roma tomatoes, fresh cilantro, and dry oregano (if using).
To serve, scoop a generous portion of rice onto each plate. Top with the Lomo Saltado mixture and arrange the crispy potatoes alongside. Garnish with green onions if desired. Enjoy your delicious and hearty meal!
