Add the onion, ginger, garlic, chilies, curry powder and sugar to a blender or food processor fitted with a blade attachment. Puree until the mixture is smooth. The mixture can be made ahead of time and stored in an airtight container for up to 3 days ahead of time.
For assembly:
Heat a large heavy bottomed-pot or Dutch oven over medium heat, add the vegetable oil and heat through. Add the curry paste and fry, stirring frequently to prevent from burning, until the curry paste darkens in color slightly, about 10 minutes.
Add the tomatoes and cook for an additional 2 to 3 minutes then add the coconut milk, lemongrass and lime leaves (if using).
Bring the mixture to a boil, then lower heat and simmer, stirring occasionally until the broth thickens slightly, about 15 minutes.
Season with salt then add the chickpeas, and cook until the chickpeas are tender, about an additional 15 to 20 minutes. Remove the lemongrass stalk and lime leaves and discard (if using) then stir in the lime zest.
Divide chickpea curry among bowls and garnish with the cilantro. Serve with the Thai basil (optional), lime wedges and naan.