In a pot, bring water to boil. Then add a little amount of salt and squeeze the quartered lemon into the pot.
Add the shrimp and simmer for 5 minutes. After 5 minutes, drain the shrimp and set aside.
In a bowl, mix the shrimp, chopped celery, chopped onion, salt, ground black pepper, mayonnaise, and mustard. Then mix well and cover it.
Store it in the refrigerator for 30 minutes.
Serve it with fresh chopped parsley on top.