First make the pangrattato by blitzing the bread into breadcrumbs in a food processor.
In a frying pan, over a medium heat, heat a tablespoon of the olive oil and fry the breadcrumbs with the garlic until golden brown and crisp.
Cook the spaghetti in well-salted, boiling water until al dente.
Put the mackerel, capers, chilli flakes, lemon zest and juice, most of the parsley and half the olive oil into a large mixing bowl and combine thoroughly.
Drain the pasta, reserving a little of the water, and add it to the mackerel mixture.
Mix vigorously, adding a little pasta water and more olive oil if it seems too dry.
Serve on a large platter, topped with the pangrattato and the rest of the chopped parsley.
