Cut the chicken into 3 cm (1 1/4 inch) cubes. Mix with half the Greek yogurt, the lemon juice, ginger, garlic, smoked paprika, cumin, curry powder and salt. Marinate in the fridge for at least 30 minutes or up to 24 hours. Soak wooden skewers in water at the same time.
Rinse the basmati rice and cook it in 480 ml (2 cups) of water: bring to a boil over high heat, cover, simmer on low for 15 minutes and rest 5 minutes.
Preheat the grill to high, about 230 to 260°C (450 to 500°F), and oil the grates. Or preheat the oven broiler to high, about 260°C (500°F), with a rack 10 cm (4 inches) below.
Thread the chicken onto the skewers, leaving small gaps between pieces so they cook evenly.
Grill or broil for about 12 minutes, turning every 3 minutes, until charred in spots and 74°C (165°F) inside.
For the raita, squeeze the grated cucumber dry and mix it with the rest of the yogurt, chopped mint and a pinch of salt.
Serve the skewers with the rice, raita, sliced red onion and tomato wedges.