Whisk all marinade ingredients together and pour over thinly sliced flank steak. Gently toss with your hands to evenly coat the steak. Refrigerate for at least 2 hours or up to overnight.
Whisk light mayonnaise with 1 tbsp gochujang until well combined. Set aside in refrigerator.
Heat a large skillet over medium-high heat (7 of 10). Add half of the vegetable oil and swirl to coat the skillet. Once the oil is shimmering and hot, add marinated steak in a single layer, being careful not to overcrowd the skillet. Cook on one side for about 2 minutes or until sugar has begun to caramelize and brown. Flip and cook 1-2 minutes on other side, or until cooked through. Wipe out pan and repeat process (you may need to do this a 3rd time depending on the size of your skillet).
Add rice, red cabbage, kimchi, carrots, and cucumber in a serving bowl or meal prep container. Add cooked bulgogi steak, then top with gochujang mayo, sesame seeds, and green onions before serving.