Combine all the ingredients, except corn starch, for marinade in a bowl and whisk them together until fully combined.
Place your chicken drumsticks in a gallon zip-lock bag. Pour marinade into the bag as well and close it. Make sure to get the air out of the bag as you close it.
Place the bag into another large dish or a bowl with the zipper up so you don't get any accidental leaks. Place it in the fridge to marinade.
Let the chicken marinade for a couple of hours OR even overnight. (You can also prep it quickly in the morning for dinner time.)
Prep the grill and get it nice and hot.
Take the chicken out of the marinade, spray it with some cooking oil spray and grill. (Save the marinade.)
(Set your coals as low from the grate as possible so you let the chicken cook instead of burn. I even cook it on the warming rack, with lid closed, to give chicken some extra distance from the coals.)
Cook chicken for 15-25 minutes, depending on the thickness of the chicken drumsticks. (Until thermometer reads 185 degrees, inserted into the thickest part.)
For the coating sauce: use the marinade that you've set aside. Add corn starch, mix it well and bring to simmer either on the grill or on the stove. If using the grill to heat the sauce, make sure to use a small, thin, metal pot. Cook the sauce, stirring often, until it is thickened. Take off heat once thickened.
Place cooked chicken drumsticks in a bowl and toss them with the thickened sauce.