Mince the onion and garlic. Dice the tomato into 1cm cubes.

Separate the mackerel from its can juice.

Heat olive oil and garlic in a pan over low heat until fragrant. Add onion and sauté until softened. Add tomato and cook until reduced.

Add mackerel and break it apart while stirring. Add chickpeas, water, and the reserved can juice. Cover and simmer over medium heat for 5 minutes.

Add curry roux and stir until thickened, about 3 minutes. Mix in butter until melted.