Heat olive oil in a large pot or Dutch oven over medium heat. Add onion and cook until softened, about 5 minutes. Add garlic and ginger and cook for 1 minute more, until fragrant.
Stir in curry powder, cumin, turmeric, and red pepper flakes (if using). Cook for 1 minute, stirring constantly, until fragrant.
Add diced tomatoes (with their juice), chickpeas, and vegetable broth. Bring to a simmer, then reduce heat and cook for 20 minutes, or until the sauce has thickened slightly.
Stir in coconut milk and spinach. Cook until the spinach is wilted, about 2-3 minutes. Season with salt and pepper to taste.
Serve hot, garnished with fresh cilantro and lemon wedges, if desired. Serve with rice or naan bread.
Notes
This curry can be stored in the refrigerator for up to 3 days.