To make the lime dressing, place the green onion, coriander, lime juice, sugar, salt and pepper in a small bowl and whisk well to combine. Set aside.
Place a large saucepan half-filled with water over high heat and bring to the boil. Line a large (or 2 small) steamer with non-stick baking paper. Place the sweet potato in the steamer, top with the barramundi and cover with a tight-fitting lid. Place the steamer on top of the saucepan and steam for 5–6 minutes. Add the snow peas and steam for a further 2 minutes or until the barramundi is cooked through. Spoon over the lime dressing to serve. Serves 2.