In a large bowl, combine soy sauce, fish sauce, minced garlic, chopped lemongrass, brown sugar, black pepper, and vegetable oil, mixing well. Add thinly sliced beef to the marinade, ensuring each piece is fully coated. Cover the bowl with plastic wrap and refrigerate for at least 4 hours, preferably overnight.

Rinse 2 cups of jasmine rice under cold water until the water runs clear. In a medium pot, combine the rinsed rice with 4 cups of water and a pinch of salt. Bring to a boil, then reduce the heat to low, cover, and simmer for 15-20 minutes until the rice becomes tender and fluffy. Let it sit covered after cooking.

Preheat your grill to medium-high heat. Take the marinated beef out of the fridge to reach room temperature for 30 minutes. Grill the beef for about 3-4 minutes on each side until a smoky char forms and the meat is juicy but cooked through.

Once grilled, let the beef rest for a few minutes before slicing it into bite-sized pieces. On a plate, scoop a generous serving of fluffy jasmine rice as the base. Arrange the sliced grilled beef on top and garnish with optional pickled vegetables, fresh cucumber slices, crushed peanuts, and drizzle with nuoc cham.