Preheat the oven to 425°F/220°C/Gas Mark 7, no fan (if you have a convection oven, reduce the temperature by about 20°).
Whisk the olive oil with the spices. This ensures that the spices are evenly distributed.
Cut the cauliflower head into steaks. You can also just divide the cauliflower into florets and roast it this way. Use a big knife to cut out the outer leaves then trim the bottom of the core, but just a little! You need a big part of the core to hold the steaks together. First, slice the cauliflower head in the middle in two, then cut 1-1.5 inch/2.5-3 cm slices. You'll have some florets left, you can arrange them with the cauliflower slices on the tray or use them to make another dish. Don't throw out the leftover stem, it's edible and also delicious. Peel it and slice into 1/2-inch/1.5cm slices and bake with the steaks.
Place the cauliflower on a baking tray and rub with the spice mixture thoroughly on all sides.
Bake for about 20-25 minutes or until golden brown and fork-tender.