Cook the shell pasta according to the package directions until al dente, being careful not to overcook. Drain and rinse under cold running water to stop the cooking process.

In a small bowl, whisk together the light mayonnaise, plain yogurt, lemon juice, fresh dill, salt, and black pepper until smooth.

In a large mixing bowl, combine the cooked pasta, drained tuna, frozen peas, diced celery, and chopped red onion. Pour the dressing over the top and toss gently until everything is evenly coated.