Cut chicken into 2.5cm cubes. Put the onion, garlic, ginger and lemon juice in a blender; puree until smooth. Empty paste into a large non-reactive bowl. Add yoghurt, coriander, salt and cumin; mix well. Add chicken pieces; turn until well coated. Cover; refrigerate overnight.
Remove chicken from marinade, discarding marinade; thread pieces on skewers. Cook on a grill or under a broiler, turning frequently, 10 to 12 minutes. Serve sprinkled with chopped mint or coriander.