Citrus and Red Onion Salad

Name: Citrus and Red Onion Salad
Ingredients: 1/4 cup thinly sliced red onions; 1/4 cup red wine vinegar; 3 medium or 4 small oranges (ideally a mix of blood orange, navel, and Cara Cara), peeled and cut into segments or rounds; 2 tablespoons olive oil; 1/4 teaspoon salt, plus more for seasoning; Dash of freshly ground black pepper, plus more for seasoning; 1/4 cup chopped green olives; 2 tablespoons chopped pistachios; 1/2 tablespoon packed tarragon; 8 ounce burrata (optional); Crackers, for serving (optional)