To make the spice rub, place spring onions, garlic, ginger, lemon juice, chopped coriander and both oils in a small blender and process until a smooth purée forms. Stir through the spices and the salt. Rub this mixture into the chicken and leave to marinate for at least an hour; for best results leave overnight.
Place chicken pieces on a plate deep enough to hold juices from the steaming process. Put the plate into a steamer and steam for 30 minutes. Remove the plate, let it stand for 5 minutes, then remove the chicken pieces to a clean plate, reserving the cooking juices. Carefully pat dry the chicken with paper towel without removing the spice mixture.
For deep frying, use a wide saucepan with very high sides. Add oil about 4cm deep. Heat the oil slowly on a medium heat and when it starts to shimmer (or reaches 170°C on a thermometer), carefully place chicken into the oil in batches to fry. Fry for about 2 minutes on each side then remove and drain on paper towels.
To make the aioli, simply whisk the mayonnaise together with the crushed garlic, lemon juice and seasoning.
To serve chicken cut each piece in half at the joint. Serve with the reserved juices.