Bring a large pot of salted water to a boil. Cook pasta for al dente texture, according to package instructions. Drain, then rinse under cold water.
In a large serving bowl, combine pasta, young peas, onion, parsley and the tuna.
To prepare dressing, in a separate bowl, whisk together the vinegar, mustard and the salt and pepper to taste. Once combined, slowly whisk in the olive oil. Toss dressing with pasta and ingredients. Serve refrigerated or at room temperature.