Pre-heat oven to 425F
Combine all ingredients and simmer on medium-low heat, allowing the guava paste to dissolve (use a fork to break it down). let it simmer out until it is smooth and thickened and turn off the heat.
Place chicken on a lined sheet pan (even better if you have a rack), skin side up. Be sure to season both sides of the chicken and roast the thighs until the juices run clear and there's an internal temperature of 165F. Brush the thighs with the glaze right before pulling them out of the oven and allow them to rest 5 minutes before serving. Garnish with sesame seeds and sliced scallions.
NOTE: it's important to rotate your pan about halfway through roasting