Place dry red chillies, fenugreek seeds, mustard seeds, fennel seeds and onion seeds in a grinder. Grind coarsely. Place yogurt and ground spices in a large bowl. Mix well.
Slit the green chillies length wise, keeping the stems intact.
Put green chilies and chicken into the yogurt mixture.
Toss to coat evenly. Refrigerate for 1 hour to blend flavors.
Heat oil in a deep pan or skillet over medium high heat.
Saute onion in oil until or crisp-tender. Add ginger garlic paste. Cook and stir for 1 minute or until its become lightly browned.
Season with chili powder, coriander powder, turmeric powder and salt. Add chicken along with the marinade.
Add 1 cup water and mix well.Bring to a boil. Cover and cook for 15 minutes or until chicken is no longer pink.
Turn the heat off. Transfer into a serving dish. Achari Chicken is ready to serve. ENJOY!!