In a medium mixing bowl, combine tuna, mayonnaise, and onion. Season with salt, pepper, and paprika. Mix well and set aside.

Slice cucumbers into ¼-inch rounds and arrange half on a serving platter.

Spread a dollop of tuna mixture on each cucumber slice, about a tablespoon per slice.

Top with remaining cucumber slices to form sandwiches and press gently to adhere.

Serve immediately or store properly for later.