Slice cooked (cold, leftover) asparagus into 1½ inch slices on an angle.
Remove the core from the pepper and cut top to bottom into about 6 sections. Slice each section into thin (about ⅛ inch) strips.
Place the vegetables in a bowl with a paper towel to dry the vegetables so the dressing will stick better. (optional)
Prepare the Dressing
Place the Dijon mustard into a small bowl. Add about ½ teaspoon vinegar. Mix well. Add another small amount of vinegar. When the mustard is thinned, add the salt and the rest of the vinegar. (This step is optional but eliminates Dijon clumps!)