1. Heat some olive oil in a pan and add in the lemongrass, lime leaves and chilies for a few minutes. Add the Tom Yum paste and cook gently for another few minutes. 2. Slowly add the coconut cream and a squeeze of lime juice. Add the mackerel and a handful of fresh coriander leaves. 3. Cook on a low heat for around 30 minutes - the consistency should be thin. 4. Garnish with some extra chilies and fresh coriander leaves. 5. Serve with a wedge of lime.