Combine lemon juice, salt, pepper and mustard in a medium-mixing bowl and whisk to mix. Whisk in oil in a slow stream so that the dressing does not separate.
Immediately pour half of the dressing on the shrimp. Fold the shrimp and dressing together with a rubber spatula to make sure they are evenly coated. Cover and refrigerate.
Combine all remaining ingredients in a large mixing bowl and fold in the remaining dressing with a large rubber spatula. Cover and refrigerate.
About half an hour before serving, add the shrimp to the vegetable salad and fold together with a rubber spatula. Taste for seasoning and add more salt, pepper or lemon juice as needed. Serve immediately.
Notes
*If preparing this recipe asĀ GLUTEN-FREE, just make sure you're using a brand of Dijon that is designated as GF.