Place your skewers in water to soak. This helps to stop them from burning too quickly during cooking. Finely grate the zest from the lemon and set aside. Squeeze the juice.
Combine half the juice with half the yogurt, the tikka masala spices and a pinch of salt and pepper in a medium bowl. Add the chicken fillets and stir to coat. Set aside to marinate while you prepare the rest of the salad.
Halve the cucumber. Halve one chunk lengthways and slice thinly (the other half will keep in your fridge for a few days). Place the sliced cucumber in a colander in the sink or over a bowl. Sprinkle with a good pinch of salt and set aside for 15-20 mins to drain.
Peel and thinly slice the red onion. Roughly chop the lettuce. Halve, deseed and dice the chilli. Roughly chop the coriander, leaves and stalks.
Heat the grill to medium and line the pan with foil. Thread the chicken fillets onto the skewers and grill for 12-15 mins, turning once, till lightly charred and cooked through – any juices should be clear when the meat is pierced.
Pat the cucumber dry with kitchen paper (the salt should have washed away with the juices). Combine with the onion, lettuce and chilli in a large bowl.
Whisk together the lemon zest, remaining lemon juice and 1 tbsp olive oil to make a dressing. Pour over the salad. Scatter with the coriander and toss to mix.
Divide the salad between 2 plates. Serve with 2 chicken skewers each on top and a dollop of the remaining yogurt on the side.