Pop the skewers in a dish of water and leave them to soak (this helps stop them catching and burning when you grill the chicken skewers).
Tip the tikka masala spice mix into a bowl. Add 1 tbsp of the yogurt. Peel and grate the garlic and ginger into the bowl. Add a good pinch of salt. Mix well. Add the chicken breast mini fillets and stir to coat them in the marinade. Set aside to marinate for 10 mins.
Coarsely grate the courgette. Place it in a sieve or colander and add a large pinch of salt. Set over the sink or a bowl. Squeeze the courgette strands a few times to remove some of the water. Pop a saucer on top of them and weigh it down with a tin or weight. Set aside to drain.
Rinse the rice under cold water. Set a small pan over a medium heat. Add ½ tbsp oil and the mustard seeds. Fry for 30 seconds. Tip in the rice. Cover with 300ml boiling water and add a pinch of salt. Cover. Bring to the boil, then turn the heat right down. Simmer for 8 mins till all the water is absorbed.
While the rice simmers, heat your grill to high. Line a grill pan or baking tray with foil. Peel and thickly slice the onion. Thread the chicken on to skewers, adding a cherry tomato and a slice of onion now and then. Lay the skewers on the tray and scatter the remaining tomatoes and onion around them.
Slide the chicken skewers under the grill for 12 mins, turning them over now and then. The edges should be lightly charred and the chicken cooked through.
While the skewers cook, check the rice. It should have soaked up all the water by now. Take it off the heat. Finely grate in the lemon zest and squeeze in the juice from half the lemon. Pop the lid back on and set aside to steam and infuse for 5-10 mins.
While the rice and skewers are finishing, make your courgette raita. Finely chop the coriander stalks, keeping them separate from the leaves. Squeeze the courgettes one more time to remove any water. Place in a bowl. Stir in the coriander stalks and remaining yogurt and sprinkle in 1 tsp black onion seeds. Add 1 tbsp lemon juice and stir. Taste and adjust the seasoning.
Serve the skewers with the lemony rice, courgette raita and the grilled veg, sprinkled with the last of the black onion seeds and the coriander leaves.