In a medium bowl, whisk together soy sauce, sesame oil, brown sugar, minced garlic, grated ginger, rice vinegar, and red pepper flakes until well combined. Add the sliced flank steak to the marinade, ensuring it’s well coated. Cover the bowl and refrigerate for at least 30 minutes, or up to overnight.

While the steak marinates, cook your rice according to package instructions. Fluff the rice with a fork and keep warm until you’re ready to assemble your bowls.

Preheat your grill or skillet over medium-high heat. Remove the flank steak from the marinade and cook for 5-7 minutes on each side for medium-rare. Let it rest for 5 minutes before slicing.

Place a generous scoop of warm rice at the bottom of each bowl. Thinly slice the rested steak against the grain and arrange it over the rice. Add kimchi, sliced cucumbers, julienned carrots, and avocado on top.

Sprinkle chopped green onions and sesame seeds on top. Optionally, add cilantro. Serve immediately while warm.