Gather all ingredients on a clean surface.
Dice the cooked ham into small cubes and place them in a mixing bowl.
If using frozen peas, thaw them in warm water and drain.
Add the peas to the bowl with the ham.
Dice the celery and chop the green onions, then add them to the mixture.
In a separate bowl, combine the mayonnaise and Dijon mustard, mixing until smooth.
Pour the mayo mixture over the ham and vegetable mixture.
Stir everything gently until well combined.
Season with salt and pepper to taste.
Chill in the refrigerator for at least 30 minutes before serving.