Cook the pasta shells according to package directions until al dente. Drain, rinse under cold water to stop cooking, and drain well again.
Toss the cooled pasta with canola oil in a bowl to prevent sticking. Set aside.
In a 2.5 to 3-quart clear glass serving bowl, place the shredded lettuce as the bottom layer.
Layer the pasta evenly over the lettuce.
Arrange the sliced hard-boiled eggs on top of the pasta and season with the salt and pepper.
Add a layer of shredded chicken followed by a layer of thawed green peas.
In a small mixing bowl, whisk together the mayonnaise, sour cream, Dijon mustard, and dried onion flakes until smooth.
Carefully spread the dressing mixture over the top layer of peas, sealing the salad to the edges of the bowl.
Cover and refrigerate for at least 2 hours (or overnight) to allow flavors to meld and the salad to chill thoroughly.
Just before serving, sprinkle the top with shredded cheese and minced parsley.