Tip the chicken into a large bowl. Peel and grate the garlic. Add to the bowl. Zest the lemon and place it in a separate bowl.
Cut the lemon in half and squeeze the juice of one half into the bowl with the chicken. Drizzle in 1 tbsp olive oil. Sprinkle in 1 tsp ground cumin. Season with salt and pepper and mix together. Set aside to marinate for 5 mins.
Peel and thinly slice the onion. Halve the tomatoes. Add both to a small bowl. Squeeze over the remaining lemon half. Add a pinch of salt and toss together. Roughly chop the mint leaves. Add to the tomato salad. Set aside.
Heat the grill to medium-high. Cut the courgette into 1 cm thick rounds. Thread the chicken onto some skewers, adding a courgette slice every now and then. Place on a baking tray lined with foil. Slide under the grill and cook for 10-12 mins till cooked through and slightly blackened. Turn once or twice to cook evenly.
Tip the yogurt into the lemon zest bowl. Mix with a little salt and pepper and a pinch of cumin.
Wrap the tortillas in foil. When the chicken has nearly finished cooking, place the tortillas under the grill pan and leave them there to warm for 2-3 mins.
Unwrap the tortillas. Spread a little of the yogurt on each one. Add a handful of the tomato salad.Using a fork, slide the chicken and courgette from the skewers and pile on top of the salad. Wrap up and eat.