Preheat oven to 400 degrees. Line a rimmed baking sheet with foil, then spray the foil with cooking spray. (I'm not kidding: The marinade is sticky stuff that you are not going to want to scrub off of a pan!)
Whisk together honey, Sriracha, balsamic vinegar, soy sauce, garlic, and oil in a large bowl. (Taste the marinade at this point to see if it's the right balance of sweet & spicy for you -- add a little more honey if you want it sweeter; add a little more Sriracha if you want it spicier.) Pour half a cup of the marinade into a small saucepan and reserve.
Trim excess skin off drumsticks, if necessary, then add them to the bowl with the marinade ingredients. Toss to coat and let the chicken sit for 15 minutes, turning over a couple of times to ensure that the drumsticks are well-coated with marinade.
Remove the chicken drumsticks from the marinade, arrange them in a single layer on the prepared baking sheet, and cook at 400 degrees for 20 minutes.
While the chicken is roasting, simmer the reserved half cup of marinade in a small saucepan over medium-low heat until reduced and thickened (about 15 minutes). You're going to use this reduced marinade to baste the chicken a few times, so that you get some nicely caramelized layers of flavor.
After drumsticks have roasted for 20 minutes, remove them from the oven and brush each with the reduced marinade. Flip drumsticks carefully with tongs and brush the other side with marinade, then return to the oven for 10 minutes.
Repeat the process: Remove chicken from oven, brush with marinade, flip and brush the other side with marinade, and return to oven for another 10 minutes. (So you're roasting the drumsticks for 40 minutes total: 20, then 10, then 10.)
Remove drumsticks from oven and brush both sides with the last of the marinade. Return them to the oven and broil for one minute to brown nicely, then serve your sticky balsamic chicken drumsticks topped with green onions and/or sesame seeds (optional).
Notes
Cooking times may vary depending on the size of your drumsticks, so check for doneness with a meat thermometer and adjust as necessary.