I buy tandoori spice mix in the UK but I think you would get a good result by grinding cumin, coriander, turmeric, cardamon and chilli, though you wouldn’t get the red colouring.
Early in the morning I mix yogurt, the juice of a lemon and spice mix. I make deep slashes in the skinless chicken thighs and marinade them in the yogurt. (I cover the bowl with cling film and put it in the fridge). At lunchtime, I lift them out of the marinade and put them in a roasting tray. I season with salt and a dribble of olive oil. They go into a preheated oven at 200°C. After 20 minutes I turn them over and add a little more of the marinade on top. In another 20 minutes or so, they should be cooked. Meanwhile, I slice two large peppers on the mandolin and cook briskly in olive oil in a non-stick frying pan. I stir fry the vegetable until any liquid has gone and the peppers have softened and taken on a little colour.
Be warned! The kitchen, your clothes and hair will smell of curry for a day, but it’s worth it!