Place eggs in a pan cover with cold water and bring to a boil.
Cover pan and turn off heat. Let sit for 8 minutes.
Fill pan with cold water to stop cooking.
Peel eggs, roughly chop and place in a bowl.
Add mayonnaise, mustard, chives, salt and pepper.
Gently mix.
If mixture is too dry, slowly add a little more mayonnaise.
Garnish bread with arugula and place half the mixture on each sandwich.