Transfer chicken chunks to a mixing bowl and add all the ingredients listed for the marinade in a bowl except for the egg, cornstarch, and rice flour and mix it well. Coat chicken pieces well with the marinade. For best results let it marinate overnight, however, I would recommend marinating for a minimum of 30 minutes.
Preheat the oven to 400 F. After the chicken has marinated, add in the beaten egg, cornstarch, and rice flour. Mix well. ( The batter should coat the chicken pieces well, if there is too much moisture, add more rice flour or cornstarch, if it's too dry, sprinkle very little water, enough to let the flours coat the chicken well).
Place the chicken pieces on a greased wire rack above a baking tray. You can also place them on a greased baking tray or a greased parchment paper/foil. Brush the chicken pieces with oil and bake for 18- 20 minutes turning once in between or until the chicken is cooked through. Broil the chicken for an additional 3-4 minutes. Cooking times may vary depending on your oven and the size of the pieces, so keep an eye. You can serve it as it is now with some lemon wedges and onion rings, or continue a step further to make the sauce to coat the pieces.
When the chicken is almost done, start with the tempering. First in a bowl combine the red chilli sauce, tomato ketchup, garam masala, sugar, salt, and pepper. Whisk well to combine everything.
Heat oil in a wok, add mustard seeds, when they splutter add minced ginger, garlic, slit green chillies, dry red chillies, and curry leaves. Sauté until curry leaves, chillies are crisp and the ginger-garlic is fragrant.
Add Kashmiri red chilli powder, cook on medium low heat for another 15 seconds.
Immediately add in the prepared sauce mixture along with 1/3 cup water, cook on medium heat until it bubbles and thickens a little. Now, add lemon juice/ vinegar and mix.
Add in the cooked chicken pieces and toss to coat evenly with the tempering and sauce. Sprinkle some chopped cilantro, and serve immediately with some onion rings and lime wedges