Preheat the oven to 180C/350F/Gas 5.
Place the beetroot in a roasting tin with the olive oil and splash of water. Cover with foil and bake for around 1 hour or until tender. Once cooked, rub off the skins (wearing gloves to protect your hands), then cut into segments and toss with a little salt and red wine vinegar. Set aside.
Heat a frying pan over a medium heat, then add the coriander, cumin, mustard and fennel seeds and toast for three to four minutes until fragrant. Leave to cool slightly, then crush in a pestle and mortar with the ginger, turmeric and a pinch of salt.
Rub a little olive oil over the salmon steaks, then pat on the spice rub. Roast on a baking sheet in the oven for 7-10 minutes until just coral-pink in the centre. Meanwhile, stir the mint leaves into the yogurt with a pinch of salt. Set aside.
Serve the salmon alongside the beetroot and rocket leaves, garnished with a spoonful of yogurt.