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 tomatoes and cook until they soften, about 3-4 minutes.
Stir in the curry powder, ground turmeric, ground coriander, and ground cumin. Cook for a few minutes until the spices are fragrant.
Add the beef pieces to the pot, stirring to coat them with the spice mixture. Cook until the beef is browned on all sides.
Add the cubed potatoes and chopped green chilies (if using) to the pot.
Pour in the coconut milk and season with salt and black pepper to taste.
Bring the mixture to a boil, then reduce the heat to low and simmer for about 30-40 minutes, or until the beef is tender and the potatoes are cooked through.
Garnish with fresh cilantro if desired.
Enjoy your meal!