Peel eggs and place in a bowl. Chop/mash with fork, leaving some bigger pieces. Add the herbs, scallions, mayo, lemon juice, mustard, salt, and pepper. Mix well, taste, and add more salt/pepper as desired (see note).
Assemble sandwich with an extra slather of mustard as desired.
Notes
+ I'm always adjusting the amount of salt, pepper + mustard based on my taste. Play around with the amounts and adjust as desired.