Skin the mackerel and check the fish for small bones. Flake the flesh into a small bowl.
Heat the olive oil in a large, shallow pan over a medium heat. Add the onion and garlic, then sauté or 5 mins, until the onion has softened Add the coriander, turmeric and curry powder and stir for a few seconds.
Add the peas and about half a cup of water. Put a lid on and steam for 3 minutes. Season with slat and pepper, then stir in the rice.
Keep stirring gently until well combined, then fold through mackerel and the herbs.
Serve warm or at room temperature.