Preheat oven to 200°C / 180°C fan-forced
Mix all coriander yogurt ingredients together and keep refrigerated until ready to serve alongside chicken.
Combine garlic, ginger, cumin, garam masala, fenugreek leaves, chilli and olive oil in a mortar and pestle and smash until it forms a paste.
Divide the spice rub into two, rub one half over chopped onions and tomatoes and use the other half to rub over the chicken thighs.
Using an oven tray lay down onions, top with tomatoes, then season with salt and pepper. Place chicken thighs on top and then season chicken with salt and pepper. Roast for 45 - 50 minutes.
Serve the roasted chicken along with the spiced oil roasting pan juices and the coriander yoghurt.