Heat oil in a wok and cook chicken until no longer pink, then add ginger and garlic paste.
Add turmeric and cook for 15 seconds, then add remaining spices and chopped green chili. Stir well.
Add tomato halves, pour in water, and cook covered for 5-7 minutes.
Peel off tomato skins if using fresh tomatoes or add canned tomatoes.
Mash tomatoes slightly with a spatula and cook covered for 15 minutes.
Remove lid, turn up the heat, and stir until water evaporates and oil separates from the curry. Lower heat.
Add black pepper and chopped green chili, mix well, and simmer on low heat.
Garnish with ginger slices and chopped cilantro. Serve with naan.