Heat your oven to 200°C/Fan 180°C/Gas 6. Break the cauliflower into small bite-sized florets. Peel and thickly slice the onion. Tip into a bowl. Dust over 2 tsp of the cumin. Drizzle over 1/2 tbsp oil. Season and toss together.
Tumble the cauliflower and onion onto a baking tray. Slide into the oven and roast for 20 mins.
While the veg are roasting, slice the kale leaves off the thick cores. Finely shred the kale leaves into ribbons and finely slice the cores. Warm a frying pan over a medium heat. Add the kale leave sand cores with 2 tbsp cold water and cook for 3-5 mins, stirring, till it’s just wilted. Take off the heat.
After the cauliflower has cooked for 20 mins, place the salmon fillets on the tray, skin side down. Return the tray to the oven and roast for another 12 mins till the salmon is pale pink and flakes easily when pressed with a fork.
While the salmon roasts, cut the ends from the oranges. Stand them on one of the cut ends. Carefully slice off the skin and as much white pith as possible. Thinly slice the oranges.
Peel and grate the ginger. Pop in a bowl. Add the tahini. Whisk in 5 tbsp cold water. Season with salt and pepper.
Stir the gingery tahini dressing through the kale. Warm over the hob for 2-3 mins, stirring, till the kale is heated through.
Toss the roast cauliflower and onion with the warm kale. Spoon into two bowls. Place a salmon fillet on top of each one (the skin may be left behind on the baking tray, which is fine) and add a few orange slices to serve.