In a large mixing bowl, combine the coconut milk, lemon juice, minced garlic, ginger, and spices including garam masala, black pepper, turmeric, and salt. Mix until well combined. Add the chicken pieces and ensure they are fully coated with the marinade. Cover and let it marinate for at least 30 minutes. For best results, marinate overnight in the fridge.

In a large pot or skillet, heat 2 tablespoons of coconut oil over medium-high heat. Once hot, add the marinated chicken in batches to avoid overcrowding. Cook for about 3 minutes on each side until browned. Remove and set aside.

In the same pot, add the remaining coconut oil. Once melted, add the diced onions and cook until they become translucent, about 5-7 minutes. Stir in the minced garlic, ginger, and diced chili. Cook for an additional minute until fragrant.

Reduce the heat to medium-low. Stir in the tomato paste, garam masala, ground coriander, cumin, and black pepper. Cook for about 2-3 minutes, stirring constantly. If the mixture appears dry, add 1-2 tablespoons of water.

Pour in the water, sugar, and salt. Let the mixture simmer over medium heat for at least 15 minutes, allowing it to thicken and deepen in color.

Remove the pot from heat. Carefully transfer the sauce to a blender or food processor. Blend until smooth, working in batches if necessary. You can also use an immersion blender directly in the pot.

Pour the blended sauce back into the pot. Stir in the remaining coconut milk or cream until fully combined. Add the browned chicken and let it simmer over medium-low heat for another 10 minutes.

Stir in the dried fenugreek or kasoori methi if using. Serve hot, topped with fresh cilantro, alongside a bed of fluffy rice or cauliflower rice.