Add cooked pasta to large mixing bowl and set aside.

Into small mixing bowl, grate onion and add apple cider vinegar, olive oil, salt, pepper, garlic powder chili pepper flakes. Squeeze 1 half of lime into mixture and whisk ingredients together until fully combined. Taste and adjust salt.

To medium mixing bowl, combine scallions, celery, spinach, sweet peppers, carrot, sun-dried tomatoes and optional veggie add-ins, if using. With fork, flake tuna out of cans into veggies. Squeeze in other half of lime, add 2 tablespoons vinaigrette and mix everything together. (Note: You have the option of draining oil from tuna or using it in the mix.)

Into large mixing bowl with pasta, add all the vinaigrette and all chopped veggies with tuna; combine well.

To serve, top with feta cheese and dill.

Serve hot or cold. If cold, refrigerate 30 minutes.