Pat the mackerel fillets dry with paper towels. Lightly season both sides with Umami Powder, ensuring even coverage.

Brush both sides of the fillets with olive oil and let them sit for 5 minutes to absorb the flavour.

Heat a pan or BBQ over medium-high heat. Brush the green onions with olive oil and place them on the grill.

Cook for 2-3 minutes per side until charred and softened. Remove from the grill, finely chop, and set aside.

Increase the heat to high and lightly oil the pan/grill grates.

Place the mackerel fillets skin-side down and grill for 3-4 minutes until the skin is crispy. Flip and cook for another 1-2 minutes until the fish is just cooked through.

Arrange the grilled mackerel on a serving plate. Top with the green onion.

Drizzle with Shiso Teriyaki just before serving.