Heat olive oil in a large lidded pan over medium heat.
Add the onions, and fry until translucent.
Add the garlic and ginger, and cook for a couple of minutes more, stirring frequently.
Add the garam masala, cumin and cayenne pepper, stir so that the onions .have a nice coating of the spices, cook for just a minute until the spices are a little toasted.
Add the chickpeas and stir well so they are covered in oil and spice.
Add the tomatoes and sugar (if using), give everything a good stir, cover, and simmer for 20 minutes on low-medium heat.
Add the spinach in batches, and stir until the spinach is wilted.
At the end of cooking, add a sprinkling of fresh coriander, and a squeeze of fresh lemon juice if desired.
Serve with rice or naan.