Ingredients:
- 1/4 cup thinly sliced red onion (from 1 small onion)
- 1/4 cup red wine vinegar
- 1 1/2 tablespoons fresh lemon juice (from 1 lemon)
- 1 tablespoon Dijon mustard
- 1 teaspoon honey
- 3/4 teaspoon kosher salt
- 1/2 teaspoon black pepper
- 5 tablespoons extra-virgin olive oil, divided
- 3 ( 6.7-ounce) jars oil-packed tuna (such as Tonnino), drained and flaked into large pieces
- 1 ( 6.7-ounce) jar pitted Castelvetrano olives , drained and roughly chopped (about 1 cup
- 1 (8 1/2-ounce) jar oil-packed sun-dried tomato halves , drained and roughly chopped (about 1 packed cup)
- 3 large celery stalks with leaves, thinly sliced (about 1 1/4 cups)
- 1/2 cup loosely packed fresh basil leaves , roughly chopped (from 1 [1/2-ounce] package)
