In a large plastic bag, combine bread crumbs, flour, salt, chili powder, coriander, cumin, and garam masala. Toss well to combine.
Pour oil to a depth of about 4 inches (10 cm) in a deep, heavy saucepan and heat to 350 degrees F (180 C) on a deep-frying thermometer.
Meanwhile, put yogurt in a bowl and whisk until smooth. Dip a few pieces of chicken into yogurt, shaking off excess. Add to bread-crumb mixture and toss to coat. Place on a plate and repeat with remaining chicken, yogurt, and bread-crumb mixture.
Carefully add a few coated chicken pieces to hot oil. Cook, turning occasionally, until golden brown, 4-5 minutes. Using tongs or a slotted spoon, transfer to a plate lined with kitchen paper.
Serve hot with lemon wedges and a tomato, onion, and cucumber relish.