Scoop egg yolks into large bowl; mash well with fork. Finely chop egg whites; add to yolks.
Mix in currants, green onion, and cilantro.
Mix 1/2 cup mayonnaise and curry powder in small bowl; stir into egg mixture.
Mix in more mayonnaise by tablespoonfuls if salad is dry. Season with salt and pepper. (Can be made 3 hours ahead. Cover; chill.)
Thinly slice cucumber crosswise into half-rounds.
Place slices on paper towels to drain. Arrange toast on work surface; spread each toast slice with mayonnaise. Divide salad among 6 toast slices; top each with cucumber slices and second toast slice.
