Bring a large pot of salted water to a boil and cook the shell pasta according to package directions until al dente—this timing is crucial for the right texture in the final salad. While the pasta cooks, finely dice the celery ribs and chop the red onion, then measure out the peas. Once the pasta is done, drain it thoroughly in a colander and set aside to cool slightly. I like to rinse the pasta with cool water to stop the cooking process and make it easier to work with.

In a separate bowl, whisk together the mayonnaise and Greek yogurt until smooth and well combined. This mixture creates a creamy, tangy dressing that's lighter than mayonnaise alone. Stir in the fresh dill, salt, pepper, and lemon juice until everything is evenly incorporated. Set aside about 1/3 of this dressing to add later—this two-stage mixing method keeps the salad from becoming oversaturated while allowing flavors to develop.

In a large bowl, combine the cooled pasta, flaked tuna, diced celery, chopped red onion, and thawed peas. Toss gently to distribute everything evenly. Pour about two-thirds of the dressing mixture from Step 2 over the pasta mixture and fold together gently until all ingredients are coated. I prefer to use a rubber spatula and fold rather than toss vigorously, which helps keep the tuna chunks intact and prevents the pasta from breaking.

Cover the pasta salad and refrigerate for at least 30 minutes to allow flavors to meld and the salad to become refreshing and cold. Keep the reserved dressing in the refrigerator as well. Just before serving, gently fold in the remaining dressing from Step 2 to freshen up the salad and add extra creaminess. Taste and adjust seasoning if needed before serving.