In a large bowl, combine the beef, soy sauce, vinegar, water, bay leaves, and black peppercorns. Marinate for at least 30 minutes, or up to overnight in the refrigerator for deeper flavor.
Heat the vegetable oil in a large pot or Dutch oven over medium heat. Add the sliced onion and sauté until translucent, about 3-4 minutes.
Add the minced garlic and sauté for another minute until fragrant.
Remove the beef from the marinade (reserve the marinade) and add it to the pot. Brown the beef on all sides, about 5-7 minutes.
Pour the reserved marinade into the pot and bring to a boil. Reduce the heat to low, cover, and let it simmer for about 1.5 to 2 hours, or until the beef is tender. Stir occasionally and add water if the sauce gets too thick.
If desired, stir in brown sugar for a touch of sweetness and adjust salt to taste.
Serve hot over steamed rice and garnish with chopped green onions if desired.