For the couscous, place the couscous into a bowl with the tepid water and salt and leave it to absorb the water.
Bring a saucepan of lightly salted water to the boil and cook the cauliflower for 3-4 minutes, or until beginning to soften. Alternately, you can steam it. Drain the cauliflower in a colander and immediately transfer to a large bowl of iced water for 2-3 minutes.
Drain again, then place into a food processor with the mint leaves and olive oil and pulse until the mixture has the consistency of coarse crumbs.
Mix the cauliflower mixture into the couscous and season, to taste, with salt and freshly ground black pepper. The couscous will keep covered in the fridge for a day.
For the salsa, place the onion and celery into a bowl with the citrus juice and the passion fruit seeds and juice and leave to one side.
For the griddled turbot, lightly season the fish on both sides with salt and freshly ground black pepper and drizzle with the olive oil.
Heat a griddle pan over a high heat and cook the fish for 2-3 minutes on each side, depending on the thickness of the fillet, until cooked through. Alternatively, cook under the grill.
Meanwhile, add the parsley and walnuts to the salsa, along with the extra virgin olive oil and soy sauce. Season, to taste, with salt and freshly ground black pepper and mix well.
To serve, place some of the couscous into the centre of each plate and lay some of the watercress or rocket on top. Place a fillet of fish on top, along with any pan juices, and spoon over the salsa.