Add the green peas (pre-drain the liquid from the jar).
Chop the green onion and parsley.
Peel the pre-boiled beets and cut them into small cubes.
Combine all the ingredients of the salad in a convenient mixing bowl, season with black pepper and salt to taste.
For the dressing, mix sour cream and mustard with the grains. Season the salad, mix gently and serve.