Heat 2 tbsp oil in a large pan. Season the chicken and fry to lightly brown the meat. Transfer it to a plate.
Add the onion to the same pan with a splash more oil. Gently fry for 10 mins, stirring often.
Add the garlic, ginger, chilli and stir for 1 min. Stir in the cumin, coriander, turmeric and cardamom.
Return the chicken to the pan. Add the juice from 1 lemon and enough stock to cover the meat. Simmer for approx 10-15 mins, until the chicken is cooked.
Stir in the spinach leaves until wilted (you may need to add a little more stock) and coriander leaves. Add more lemon juice and season to taste.
To get the most juice from your lemons use them at room temperature, rather than straight from the fridge. Before squeezing, roll the lemons on a work surface, pressing them down with the palm of your hands as you roll, to release more juice.
If using baby spinach or true spinach leaves (stripped off their stalks), they can be stirred straight in. If using cooking spinach, strip off the leaves, blanch in boiling water, refresh, chop and add them at the end.