Heat oil in a large fry-pan on medium heat. Add onion and cook for 4-5 minutes until soft. If at any time onion is sticking to the bottom of the pan and burning, add 1-2 tablespoons of water, stir, and it should unstick.
Add curry paste and 3-4 tablespoons of the coconut milk, stir together until smooth and cook for 2-3 minutes until the paste if fragrant.
Add remaining coconut milk, kaffir lime leaves, sweet chilli sauce and fish sauce, stir and simmer for 3-4 minutes. Add chicken to simmering sauce, cover and cook for about 5 minutes before adding courgette, peas and beans; continue to cook for a further 3-4 minutes or until chicken is cooked through. Season to taste with more fish sauce if needed.
Scatter fresh herbs over the curry and serve with cauliflower rice. Squeeze over lime or lemon just before eating.