Ingredients (Metric & Imperial measurements):
4 Large tuna steaks - see note 1
100 ml (4 fl oz) Extra virgin olive oil
Lemon zest from one small lemon (finely chopped)
40 g (1 1/2 oz) Capers (finely chopped) - see note 2
3 g (1/2 tsp) French mustard
10 g (1 tbs) Anchovy paste
10 ml (a bit less than 1/2 fl oz) Lemon juice
Salt for seasoning