Blend the onion, ginger and chili with a splash of water in a small blender. Tip into a pan, and bring to a simmer. Add the spices with a pinch of salt, cook for a minute, then add the peppers, chicken and cauliflower, stir into the curry paste and cook for another 5 minutes.
Add the chopped tomatoes, half-fill the can with water and tip into the pan. Simmer for 25 minutes until the chicken is cooked through. Cook for another few minutes if the sauce is too thin, then stir through the spinach until wilted. Season, and serve in bowls.