Heat a large saute pan with olive oil to medium-high. Add onion and saute for 1 - 2 minutes, until translucent.
Add chicken pieces and cook for 6 – 7 minutes total, until no longer pink on the outside.
Meanwhile, in a medium bowl, whisk together soy sauce, water, gochujang chili paste, minced garlic, grated ginger, red chili flakes, vinegar, sesame oil, honey, and arrowroot starch. TIP: start with 1 tsp of red chili flakes, taste the sauce after simmering, and add more if you want it spicier.
Once the chicken is ready, reduce the heat to low and pour the bulgogi sauce on top of the chicken. Stir to combine and simmer on low until the sauce thickens slightly - for about 2 - 5 minutes. Taste and add more red chili flakes, if desired. NOTE: make sure the heat is on low, or the sauce will burn.
Meanwhile, wash lettuce. Then break off all large leaves and place them on a paper towel to dry.
Add a few spoonfuls of rice to each lettuce cup, top with warm chicken, sliced green onions, and sesame seeds. Enjoy!