- Heat the tacos according to packet instructions.
- Flake the mackerel into small pieces and combine with the red cabbage and beetroot in a large bowl.
- Mix 2 tbsp of the sour cream with the horseradish.
- To serve, spread a little of the horseradish and sour cream mixture inside the tacos and fill generously with the mackerel mixture. Top with extra sour cream, coriander and a squeeze of lemon juice.