Fill the pressure cooker with water, and add a few beetroots. Bring to a boil over medium-high heat, and cook for about 3 minutes.
Add potatoes to the water, and continue to cook for another 3 minutes. Add carrots, and continue boiling until everything is soft, about 2 more minutes.
[Note : Time may vary with the sizes of the vegetables ] Drain, and let the vegetables cool until cool enough to handle. Cut the vegetables into cubes, and place them in a serving bowl.
Stir in mayonnaise, powdered pepper and mustard until everything is well coated. Serve warm or cooled as you wish.