Combine the lemon zest, lemon juice, oil and garlic.
Cook the cauliflower in salted water for approx. 5 mins., remove and drain, allow to cool slightly. Place the cauliflower and onions in a grill tray, season with salt, mix with 2 tbsp of lemon oil.
Cover and grill the cauliflower over/on a medium heat (approx. 200 °C for approx. 15 mins. Salt the fish, brush with 1 tbsp of the lemon oil, place in a second grill tray. Grill for approx. 4 mins. on each side.
Mix the couscous and salt in a bowl, pour the water over the top, cover and leave to absorb for approx. 5 mins. Separate the couscous with a fork.
Season the remainder of the lemon oil, mix with the cauliflower florets, onions and couscous. Mix in the herbs. Divide the salmon into pieces, serve on top.