Heat vegetable oil in a medium skillet over medium heat.

Add finely chopped onion to the skillet.

Cook onion over medium-low heat, stirring occasionally, until golden brown and caramelized, about 20 minutes.

Remove the skillet from heat and let the caramelized onions cool.

Cut the hard-boiled eggs in half.

Scoop the egg yolks into a medium bowl.

Mash the egg yolks well with a fork.

Finely chop the egg whites.

Add the chopped egg whites to the bowl with the mashed yolks.

Mix in the cooled caramelized onions, mayonnaise, mustard, and curry powder.

Season the egg salad mixture with salt and freshly ground black pepper to taste.

Trim the crusts from the raisin-walnut bread slices.

Spread the egg salad evenly onto the bread slices.

Cut each sandwich diagonally to make 24 triangles.

Garnish each sandwich triangle with a fluff of clover sprouts or microgreens, if desired.