In a blender place the garlic, ginger, coriander, cayenne pepper, garam masala, cumin, turmeric, paprika, salt and pepper to taste, and blend into a paste.
Place the chicken in a bowl with the spice mix, cover and leave in the fridge for at least an hour, preferably overnight.
In a non-stick pan heat the oil and brown the chicken, then set to one side.
Add a little more oil (if needed, to the same pan and soften the onion for 5 minutes. Add in the tomatoes and spinach, and place the lid on, cooking until the spinach has wilted down. Add the chicken, cook for 10 minutes, then remove the lid and simmer gently until the chicken is thoroughly cooked.
Serve with delicious homemade keema rice and naans!