Toast the coriander seeds in a dry pan until fragrant. Crush in a pestle and mortar and mix with the sesame seeds and oats.
Put the oat mixture on a plate. Season the hake pieces, then dip them in the egg white. Roll the hake in the seed mix until fully coated. Transfer to an oiled baking tray and bake for 6 minutes.
If any mussels are opened, tap them lightly on a hard surface. If they don’t close, discard them. Put the garlic, wine, cream and mussels in a lidded saucepan. Cook over a high heat for 3–4 minutes, shaking the pan from time to time, until the mussels have opened. (discard any that don’t open). Strain the cooking liquor into the bowl of a food processor, reserving the cooked mussels.
Add the mackerel and a splash of olive oil to the food processor and blend until smooth. Add the lemon juice and blend again.
Heat the butter in a frying pan and gently wilt the spinach.
To serve, put the wilted spinach on the centre of the plates, top with a piece of hake and add a few mussels. Spoon over the mussel and mackerel velouté and sprinkle over the flowers, if using. Drape the wild garlic over the top.