In a large mixing bowl, combine the ginger, garlic, soy sauce, lemon juice and the spices (ground cumin, red chili powder, turmeric, sambhar powder and salt). Add the cornstarch and mix well to combine. Add the chicken pieces and mix to coat well. Cover, refrigerate and let marinate for at least 1 hour (the longer the better). Remember to remove the chicken from the refrigerator 15-20 minutes before pan frying to allow it to come to room temperature.
In a large wok or deep skillet on medium high heat, add 3-4 tbsp of oil. When hot, very carefully add the black mustard seeds. When the splattering subsides, add the green chilies and fresh curry leaves. Then carefully add the chicken pieces and fry until cooked through. They should be golden brown and crispy on all sides. Drain well. You may need to do this in small batches.
Sprinkle the chicken pieces with a pinch of salt when still hot, garnish with wedges of lemon and/or lime and serve with your favorite chutneys and sauces.
You can also use the chicken pieces in naans or rotis to make delicious Indian wraps. Just add some lettuce, tomatoes and red onions and then top with your favorite chutneys and sauces.