Heat the oven for 200°C/400°F. Place the mackerel on a baking sheet. Stuff the cavity of each mackerel with the lemon slices, garlic and a sprinkling of salt. Mix together the olive oil, parsley and chilli and drizzle over the fish. Place in the oven for 20 minutes.
Mix together all the ingredients for the salad in a large bowl apart from the walnuts, season to taste. Leave to sit while you wait for the mackerel to cook. Serve with a whole baked mackerel and flatbread topped with the walnuts.
Nutrition information is an estimate and will vary depending on the ingredients used.