1. Heat your oven to 200°C/Fan 180°C/Gas 6. Pop the miso in a shallow dish. Peel and grate in the ginger. Add 1 tbsp tamari. Zest and juice in the lime. Add 1 tbsp brown rice vinegar, ½ tbsp sugar and 2 tbsp cold water. Mix to make a marinade.
2. Pop the trout fillets in the dish and turn them a couple of times to coat in the marinade. Set aside while you prepare the veg.
3. Scrub, trim and slice the carrot into to thin matchsticks. Break the woody ends from the asparagus spears – bend them and they should snap off. Cut the tender spears in half widthways. Trim the roots off the spring onions and slice off any ragged tops. Finely slice the spring onions – white and green parts. Set the green parts aside.
4. Tear off 2 large squares of foil or greaseproof paper, around 15cm x 30cm. Divide the asparagus, carrots and spring onions between the 2 sheets, placing the veg in the centre.
5. Lay the trout on top of the veg. Pour the marinade over the top of each. Bring the edges of the foil or paper together and scrunch together to form a parcel, tucking the short ends underneath the parcels. Place the parcels on to a baking tray. Slide the parcels in the oven for 12-15 mins to cook the fish and veg.
6. While the trout cooks, zest the lemon. Tip the rice into a sieve and give it a good rinse. Tip it into a small pan and add 300ml boiling water, the lemon zest and a pinch of salt. Cover, bring to the boil, then turn the heat right down. Gently simmer for 8 mins till all the water has been absorbed. Take off the heat and leave to steam in the pan for 5-10 mins, then fluff with a fork and squeeze in the juice from the lemon.
7. While the rice cooks, peel and finely grate the garlic into a medium bowl. Add the remaining sugar and brown rice vinegar with a pinch of salt. Mix together well. Halve the cucumber and scoop out the seeds with a teaspoon. Slice it into thin half-moons. Add to the vinegar and sugar and stir.
8. Remove the fish from the oven. The fillets should be opaque and flake when pressed lightly with a fork. The veg should be tender.
9. Spoon the lemon rice onto warm plates. Place a tangle of watercress on each plate and top with the cucumber pickles. Lift the fish and veg from their parcels and set on the plates, spooning sauce over each. Garnish with the spring onion tops to serve.