Heat 1 tbsp of the oil in a deep frying pan over a medium heat. Brown the chicken in batches, setting aside once golden. Fry the onion for 8 minutes until softened. Then add the garlic, chilli and ginger and fry in the other 1 tbsp oil for 1 min. Add the garam masala and fry for 1 min more.
Stir in the peanut butter, coconut milk and tomatoes, and bring to a simmer. Return the chicken to the pan and add the chopped coriander. Cook for 30 mins until the sauce thickens and the chicken is cooked through.
Serve with the remaining coriander, roasted peanuts and rice, if you like.
