Heat oil in a large frying pan or skillet over medium-high heat.
Add cinnamon stick and cumin seeds. Sauté, stirring, for 1 minute.
Add onions, tomatoes, garlic, ginger and green chilies. Sauté, stirring, for about 2-3 minutes or until browned.
Add ground turmeric, ground coriander and red chili powder. Sauté, stirring, for about a minute or until fragrant.
Remove from heat.
Cool completely.
Grind to a smooth paste.
Transfer to a food processor. Grind to a smooth paste. Add water if needed.