Heat the vegetable oil in a large pot or skillet over medium heat.
Add the finely chopped onion and sauté until translucent, about 5 minutes.
Stir in the minced garlic and fresh ginger, cooking for another minute.
Add the chopped tomato and cook until it softens, about 3-4 minutes.
Stir in the curry powder, ground turmeric, and ground coriander. Cook for a few minutes until the spices are fragrant.
Add the chicken pieces to the pot, stirring to coat them with the spice mixture. Cook until the chicken is browned on all sides.
Pour in the coconut milk and add the chopped green chilies if using. Season with salt and black pepper to taste.
Bring the mixture to a boil, then reduce the heat to low and simmer for about 20-25 minutes, or until the chicken is cooked through and the sauce has thickened.
Garnish with fresh cilantro if desired.
Enjoy your meal!