Step 1Make gashes diagonally across grain of turkey flesh. Rub with lemon juice and salt and set aside.
Step 2Place yogurt in large bowl and whisk in oil, ginger-garlic paste, ground chile, paprika, coriander, mustard, pepper, garam masala and salt to taste. Coat turkey generously with yogurt mixture, making sure all parts are coated. Marinate overnight in refrigerator.
Step 3Stuff turkey as desired. Place in roasting pan and cover loosely with foil. Roast at 325 degrees until meat thermometer inserted in thigh registers 140 degrees, 3 hours. Remove foil, brush with butter and roast uncovered until thermometer reaches 165 degrees, about 20 minutes.
Step 4Remove to platter and serve hot, garnished with onions and lemon wedges. (Make gravy, if desired, using roasting juices, adding ground red chile to taste.)