Put the eggs in a large saucepan of cold water and bring to a vigorous boil. Cover, remove from the heat and let stand for 10 minutes. Drain the eggs and cool under running water, shaking the pan to lightly crack the shells. Transfer the eggs to a bowl of ice water and let stand until completely cold, about 15 minutes.
Peel the eggs and pat dry. Finely chop the eggs and transfer to a large bowl. Add the orange zest and juice along with the curry, dry mustard and mayonnaise. Season with salt and pepper and mash with a fork.
Arrange 10 slices of bread on a work surface and divide the egg salad among them, spreading it to the edges. Top with the remaining bread and trim off the crusts. Cut each sandwich in half. Transfer to a platter and serve.