Preheat oven to 230°C fan forced. Grease a large roasting pan. Place drumsticks in a single layer on a large tray. Cut 2–3 deep slashes into each drumstick (see tip).
Combine salt flakes, garlic salt, paprika and oil in a jug. Stir to combine. Remove 1 tablespoon to a large bowl. Pour the remaining oil mixture over the chicken. Rub into chicken to coat.
Place the flour in a snap-lock bag. Add drumsticks, 1 at a time, and toss to coat. Place drumsticks in roasting pan. Spray both sides lightly with oil. Roast drumsticks for 15 minutes.
Meanwhile, add 1 tablespoon lemon juice to oil mixture in the bowl. Add the mushrooms and stir to coat.
Turn the chicken drumsticks over and spray again with oil. Add the mushrooms to the roasting pan. Roast for a further 15 minutes or until chicken is just cooked through. Serve.