Cook the shells according to the package instructions, being careful not to overcook. Once done, drain and rinse the pasta with cold water to stop the cooking process.

In a small bowl, whisk together the mayonnaise, yogurt, lemon juice, dill, salt, and pepper until well combined for a smooth dressing.

In a large bowl, combine the cooked noodles, drained tuna, peas, diced celery, and onion. Mix carefully to avoid breaking the pasta or tuna.

Pour the dressing over the pasta salad mixture and toss gently until everything is well coated.