Combine all ingredients for brining chicken (besides the chicken) in a large shallow baking dish using your fingers.
Add the chicken to the mixture and rub it all over, patting to make it adhere if possible.
Set chicken on a rack on baking sheet so that any moisture can drain off, and set it in the fridge uncovered for 8-24 hours.
Remove chicken about 30-45 minutes prior to cooking to let it warm up a bit.
Preheat oven to 400 degrees. Line a baking sheet with foil and set chicken on sheet. Bake for 10 minutes.
Remove sheet pan from oven and add potatoes in between the chicken. Drizzle with a little olive oil and set back in the oven to roast for 25 minutes or until potatoes are soft and the chicken has almost reached 165 degrees (the chicken will only be cooked a few more minutes after this step so it is crucial that it has hit a high enough temperature to serve by this point. The drumsticks with cook faster since they're smaller but they're dark meat so they can handle it better).
Remove sheet pan from oven again and turn up the heat to 450 degrees. Smash potatoes using a fork or a pastry blender (if you want to, but this is unnecessary if you just like your potatoes whole).
Add asparagus in bunches wherever there is room on the sheet pan. Slice the reserved lemon (that you had zested for the brine) and lay the slices over the asparagus. Return to the heated oven for 8-10 minutes or until asparagus is tender, but not limp.
Let the chicken rest for 10 or so minutes before serving so that the juices don't run out. Season with kosher salt and pepper if necessary, and enjoy.