Heat the olive oil in a large skillet over medium heat. Add the onion and cook 5 minutes or until fragrant. Add the garlic and ginger, cooking another 2 minutes. Stir in the garam masala, curry powder, turmeric, cayenne, and a pinch each of salt and pepper. Cook until fragrant, about 1 minute. Add the chickpeas and toss to coat with the spices. Cook 5 minutes.Stir in the coconut milk, pumpkin, tomato paste, butter, and 1/2 cup water. Simmer 5 minutes, until the sauce thickens slightly. Remove from the heat and stir in the cilantro. Season with salt and pepper.Serve the chickpeas and sauce over bowls of rice with fresh naan and additional cilantro.