Heat a thick based pot or pan over a medium heat. Fry the onions in olive oil, stirring regularly, until softened but not browned, 10–12 minutes.
Add the chili (if using), garlic and spices and fry for another couple of minutes, continuing to stir regularly.
Turn up the heat and add the chicken. Fry until the chicken starts caramelising, stirring regularly.
Add water to nearly cover the chicken, (100-200 ml/⅖–⅘ cup), depending on the size of your pot or pan, and bring to the boil. Turn the heat to low, cover with a lid and leave to simmer for 10-15 minutes.
Add the peas, chickpeas (if using) and chili flakes. Gently mix and simmer until the peas are done, 3-4 minutes. The peas should still have a slight bite to them.
Add lemon zest and juice. Season. Serve warm.
