Cover a large plate with several layers of kitchen paper. Arrange the tofu on top and cover with more paper, then put a plate on top and weigh down with a tin. Allow the tofu to drain for 30 minutes, then pour off the liquid and cut the tofu into 2.5 cm (1 in) cubes.
To make the marinade, combine all the ingredients in a shallow bowl. Add the tofu to the bowl and marinate for at least 30 minutes, stirring and turning a few times.
Meanwhile, make the salsa. Mix all the ingredients together with salt to taste in a small bowl and set aside. Heat the grill or light the barbecue.
Lift the tofu out of the marinade and thread it onto skewers alternately with the mango pieces. Add the remaining marinade to the salsa.
Grill the kebabs for 6-8 minutes, turning them once or twice, until the tofu is browned and heated through. Serve hot with the salsa, garnished with the strips of spring onions, and lime wedges.
Variation: if you cannot find green unripe mango, substitute diced ripe mango in the salsa.