In a medium bowl, combine the chicken pieces with coconut yogurt, 2 minced garlic cloves, 1 tbsp grated ginger, 1 tsp garam masala, 1/2 tsp turmeric, Kashmiri red chili powder, and 1/2 tsp salt. Mix until the chicken is thoroughly coated. Cover and refrigerate for at least 30 minutes or up to 8 hours.

Heat 1 tablespoon of oil in a large skillet or Dutch oven over medium-high heat. Add the chicken in a single layer, working in batches if necessary to avoid overcrowding. Cook for 3-4 minutes per side, until browned and cooked through. Remove the chicken from the skillet and set aside.

Reduce the heat to medium and add the remaining tablespoon of oil to the same skillet. Add the chopped onion and cook until softened, about 5-7 minutes. Add the 4 minced garlic cloves and 1 tbsp grated ginger, stirring for one minute until fragrant. Stir in the 1.5 tsp garam masala, cumin, coriander, and 1/2 tsp turmeric, and cook for 30 seconds until aromatic.

Pour in the tomato passata and cook for 5 minutes, stirring occasionally. Stir in the full-fat coconut milk and 1 tsp salt. Bring the sauce to a gentle simmer, then reduce the heat to low. Return the cooked chicken to the skillet. Allow it to simmer gently for 10-15 minutes. Stir in the crushed fenugreek leaves in the last minute of cooking. Serve hot, garnished with fresh cilantro.