Whisk together soy sauce, fish sauce, brown sugar, lime juice, minced garlic, black pepper, and red pepper flakes in a medium bowl.

Place flank steak in a resealable bag, pour marinade over it, seal and refrigerate for 1 to 4 hours.

Rinse jasmine rice under cold water, combine with water in a pot, bring to boil, reduce heat, cover and simmer for 15 minutes.

Heat grill pan over medium-high heat, add vegetable oil, remove steak from marinade, grill for 4-5 minutes per side.

Let steak rest for 5 minutes, then slice against the grain.

Serve rice on a plate, top with sliced steak, garnish with cilantro and sesame seeds, and add cucumber on the side.