Make deep cuts in each drumstick to the bone so the chicken will cook more evenly. Place chicken on a plate, sprinkle with salt and pour the lemon juice into the cuts. Set aside.
In a bowl, combine yoghurt, onion, garlic, ginger, chillies, garam masala, turmeric and tandoori powder. Blend thoroughly with a hand blender until smooth.
Strain the mixture into a bowl through a sieve. Push through as much liquid as possible. Add the chicken and rub the marinade in well. Place in a baking tray, cover with foil and refrigerate overnight.
When ready to cook, preheat the oven to its hottest temperature for 20 minutes, then reduce heat to 200 degrees C.
Place the chicken into the top third of the oven. Bake 30 minutes to an hour until cooked through, checking to see if the juices run clear. Turn chicken halfway over during cooking.