Mix and Shape the Koftas — In a large bowl, combine the ground chicken, toasted besan, grated onion, ginger garlic paste, minced green chilies, chopped coriander, red chili powder, garam masala, cumin, turmeric, salt, and beaten egg. Mix with your hands just until evenly combined. Lightly oil your palms and shape into 16–18 golf-ball-sized koftas (about 1½ inches). Refrigerate 15 minutes.

Brown the Onions — Heat the oil in a wide, heavy pot over medium-high heat. Add the sliced onions and cook 8–10 minutes until deeply golden brown.

Build the Gravy Base — Stir in the ginger garlic paste and cook 1 minute. Add the chopped tomatoes, slit green chilies, red chili powder, turmeric, ground coriander, half the garam masala, and salt. Cook 6–8 minutes until the tomatoes break down and oil separates at the edges.

Add Yogurt and Water — Lower heat to medium-low, stir in the whisked yogurt a spoonful at a time, then pour in the warm water. Simmer gently 5 minutes.

Simmer the Koftas — Slide the chilled koftas into the simmering gravy, don't stir for 8–10 minutes. Cover and simmer on medium-low 20–25 minutes until cooked through (165°F / 74°C).

Finish and Serve — Sprinkle remaining garam masala, scatter coriander and sliced green chilies, simmer uncovered 2–3 minutes. Rest 5 minutes, serve hot with basmati rice or naan.