I whisk together gochujang, sugar, garlic, oil, gochutgaru, soy sauce, toasted sesame oil, salt, and optional black pepper in a mixing bowl. I taste the marinade at this stage and adjust sweetness or salt so it suits my palate.
Then I add chicken thighs cut into large pieces, coating each piece fully in that marinade. If possible, I let it marinate ahead so flavors deepen.
I heat up a cast iron grill pan (or any heavy pan) over medium-high with a bit of oil. I place chicken pieces spaced out so they can sear properly without steaming.
Each piece cooks 2-3 minutes per side until cooked through (internal temperature to safe point). I remove cooked pieces with juices and repeat until all chicken is done.
Once chicken is ready, I layer each bowl starting with hot rice, then arrange chopped romaine lettuce, shredded carrot, sliced cucumber, sliced avocado, and optional red onion. I top with the hot, marinated chicken. To finish, I sprinkle toasted sesame seeds and serve immediately while chicken and rice are hot and veggies are crisp.