In a mixing bowl, whisk together soy sauce, fish sauce, brown sugar, lime juice, minced garlic, black pepper, and red pepper flakes until well combined.

Coat the flank steak thoroughly with the marinade and refrigerate for at least 1 hour, or up to 4 hours.

Rinse jasmine rice under cold water until water runs clear, then combine rice with water in a saucepan and bring to a boil.

Heat vegetable oil in a skillet over medium-high heat until hot.

Sear the marinated flank steak for 4-5 minutes on each side until browning occurs.

Remove steak from skillet and let it rest for 5 minutes, then slice against the grain.

Serve jasmine rice topped with sliced beef and garnish with cilantro, sesame seeds, and cucumber slices.