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 (keep the rest for later), 1/2 tbsp sugar (keep the rest of this too) and 2 tbsp cold water. Mix together well. Place the haddock in the dish and turn them a couple of times to coat in the marinade. Set to one side.
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 asparagus spears in half widthways.
Tear off 2 large squares of foil or greaseproof paper. Divide the asparagus and carrots between the two sheets, placing the veg in the centre.
Lay the haddock 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. Place the parcels on to a baking tray.
Slide the fish in the oven for 15 mins to cook the fish and veg.
While the fish is cooking, 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 stir in the lemon juice.
Peel and finely grate half the garlic clove and place in a medium bowl. Add the remaining sugar and brown rice vinegar. Mix together well. Peel your cucumber. Halve it and scoop out the seeds. Cut it into thin matchsticks and add to the bowl. Using the end of a rolling pin, bash the cucumbers till a little crushed. Toss with the vinegary dressing.
Trim and thinly slice the salad onions diagonally.
Remove the fish from the oven. The fish should be opaque and flake when pressed lightly with a fork. The veg should be tender.
Spoon the lemon rice onto warm plates. Place a tangle of watercress on each plate and top with the smacked cucumber. Lift the fish and veg carefully from their parcel and place on the plate, spooning sauce over each. Garnish with the salad onions.