Whisk together yoghurt, lime juice, curry powder, ginger, salt and pepper in a large bowl.
Add oil in a slow stream, whisking until combined.
Rinse quinoa (or amaranth) in a bowl using 5 changes of water, rubbing grains and letting them settle before pouring off water (if quinoa does not settle,drain in a large sieve after each rinsing).
Cook quinoa (or amaranth) in a large pot of boiling salted water 10 minutes.
Drain in a large sieve and rinse under cold running water.
Set sieve with quinoa (or amaranth) over a saucepan containing 4cm boiling water (sieve should not touch the water) and steam the grains, covered with a kitchen towel and lid, until fluffy and dry, 10 to 12 minutes.
Toss with curried yoghurt and remaining ingredients in a large bowl.