Season the chicken pieces with salt and a teaspoon of chilly powder.
Heat oil in a kadhai or wok over medium-high heat. Add chicken and fry them on each side until browned (approximately 3-4 minutes each side). Don't overcrowd the pan, fry them in batches. Transfer the chicken to a plate and set aside.
Add the chopped onion slices and fry them till they soften (approximately 10-12 minutes). Meanwhile, grind the coriander leaves, mint leaves, green chillies and garlic cloves to a fine paste.
Add the ground paste to the onions (once the onions are done) and fry them for another 5-6 minutes.
Add the yogurt, salt, garam masala and remaining chilly powder and mix well. Add water as needed to get it to the consistency you desire.
Add the chicken back to the wok and continue cooking on medium heat till it is done (approximately 10 minutes). Cover the wok and let it simmer for another 5 minutes.