Preheat oven to 200C. Stir miso, soy, mirin and half the ginger in a small saucepan over medium-high heat until smooth and set aside.
Combine half of each oil in a large non-stick frying pan over medium-high heat, add fish and brown on both sides (1-2 minutes). Transfer to an oven tray lined with baking paper, brush thickly with miso glaze (you won’t need it all) and roast until cooked through (4-5 minutes), then scatter generously with sesame seeds.
Meanwhile, heat remaining oils in a large frying pan over medium-high heat, add greens and spring onion and stir-fry until just wilted (2-3 minutes), add garlic and remaining ginger and stir-fry until fragrant (30 seconds). Toss any remaining miso mixture through and serve greens with roast mulloway, pickled ginger and steamed rice.