Tuna Souvlaki Pasta Salad

Name: Tuna Souvlaki Pasta Salad
Ingredients: 0.5 red onion, cut into bite-size pieces; 4 cups ice water, or as needed; 1 (8 ounce) package tri-color rotini pasta; 1 (5 ounce) can light tuna in water, drained and flaked; 2 stalks celery, cut into bite-size pieces; 0.5 cup roasted red peppers, drained and chopped; 0.25 cup smoked sun-dried tomatoes; 0.25 cup crumbled feta cheese; 1 sprig parsley, stemmed and leaves minced; 4 leaves fresh basil, rolled and very thinly sliced; 2 teaspoons capers; 1 cup Greek vinaigrette salad dressing