Heat a wide-bottomed non-stick pan over high heat, then add the oil. Once hot, add the diced onion, garlic, and ginger. Fry for 2–3 minutes until they start to brown.
Add the cumin seeds, red pepper, and a pinch of salt, frying for another 2 minutes until the pepper begins to soften.
Stir in the turmeric, garam masala, cinnamon stick, and black pepper, and cook for 1 minute.
Add the vegetable stock, tamari, and chopped tomatoes, and bring to a boil. Add the baby spinach, mixing well until it wilts.
Sieve in the gram flour, stirring until incorporated. Let the curry simmer for 10–15 minutes until thickened.
Serve with toasted pitta breads or your favourite grain, topped with sliced red chilli.