Start by boiling the potatoes and carrot until they are tender.
Once cooked, peel the potatoes and carrot, and cut them into small cubes.
Boil the egg until hard-boiled, then peel and chop it into small pieces.
Drain the tuna and flake it into smaller chunks.
In a large mixing bowl, combine the potatoes, carrot, chopped egg, tuna, peas, and any optional ingredients you choose to include.
Add mayonnaise to the bowl and gently mix everything together until all the ingredients are evenly coated.
Adjust the amount of mayonnaise according to your preference for creaminess.
Season the salad with salt to taste.
Once everything is well combined, transfer the Ensaladilla Rusa to a large bowl.
Refrigerate the salad for at least an hour before serving to allow the flavours to meld together.
Plate the salad in serving dishes and garnish with slices of piquillo peppers if desired.
Serve cold.