In a mixing bowl, combine soy sauce, fish sauce, brown sugar, lime juice, minced garlic, black pepper, and red pepper flakes. Whisk until the sugar dissolves.

Place the flank steak in a resealable bag or shallow dish, ensuring it’s fully coated. Allow to marinate in the refrigerator for at least 1 hour, preferably 1-4 hours.

While the beef marinates, rinse jasmine rice under cold water until the water runs clear. Combine rinsed rice with 1 1/2 cups of water in a medium saucepan and bring to a boil.

Reduce to low, cover, and simmer for 15 minutes until water is absorbed. Fluff rice with a fork and set aside.

Heat vegetable oil in a large skillet over medium-high heat. Remove flank steak from marinade and place in the hot pan.

Cook for 4-5 minutes on each side for medium-rare, until charred and sizzling. The interior should reach 130°F (54°C).

Transfer cooked flank steak to a cutting board and let it rest for about 5 minutes to allow juices to redistribute.

Slice the flank steak against the grain into thin strips. In serving bowls, place jasmine rice and sliced beef on top. Garnish with fresh cilantro and sesame seeds. Serve with cucumber slices on the side.