Begin by boiling a large pot of salted water over medium-high heat. Once it reaches a rolling boil, add in the whole wheat rotini pasta. Cook according to the package instructions, typically around 7–9 minutes, until al dente. Once done, drain the pasta in a colander and rinse under cold water to halt the cooking process and prevent sticking.

While the pasta cools, chop the cucumber, celery, and red bell pepper into bite-sized pieces. Also, prepare the frozen peas by measuring out a cup and allowing them to thaw if needed. In a large mixing bowl, combine these colorful veggies along with the drained tuna.

In a separate medium bowl, combine the plain Greek yogurt, light mayonnaise, lemon juice, and Dijon mustard. Whisk these ingredients together for about 1–2 minutes until smooth and creamy.

Add chopped fresh dill, garlic powder, salt, and pepper to enhance the flavor of the dressing. Stir everything together well for another minute.

Pour the creamy dressing over the chilled pasta and vegetable mixture in the mixing bowl. Use a spatula to gently fold the ingredients together, ensuring every piece is well-coated.

Cover the salad with plastic wrap or a lid, and refrigerate for 20–30 minutes to allow the flavors to meld together.