How to make it
Place the beetroot with their skins and roots still on, into a pan of water and bring to the boil. If you have managed to get all three colours, (yellow, candy striped and purple), you will want to do this in separate pans so the purple ones don’t stain the others! Cook for approximately 10 minutes until tender. Remove from the pan and refresh in cold water. The skins should rub off easily now, but keep the roots on as they look pretty.
Add the soy sauce, rice vinegar, sesame oil and sugar, and put over a moderate heat for 10-15 minutes until it has reduced and turned into a thick glossy glaze. Add the beetroots to the pan and gently coat them all over with the glaze. Put to one side whilst you cook the mackerel.
Put a griddle pan over the biggest highest flame and get really hot to the point of it starting to smoke. Rub a little olive oil onto the skin side of the mackerel fillets, followed by a liberal seasoning of salt. When the pan is hot enough, place the mackerel skin side down, and fry for 2 minutes on each side.
Remove from the pan and serve immediately with the beetroots and dress some mizuna leaves with the leftover glaze a little lemon juice, salt, pepper, olive oil and a sprinkling of sesame seeds.