Beefsteak Tomato Sandwich recipes

Name: Beefsteak Tomato Sandwich recipes
Ingredients: 1 small red onion, halved and very thinly sliced; ⅔ cup water; ⅓ cup red wine vinegar; 2 tablespoons granulated sugar; Pinch kosher salt; 2 teaspoons fresh thyme; 2 teaspoons black peppercorns; ½ cup mayonnaise; 1 tablespoon Dijon mustard; 2 teaspoons capers, chopped; 2 teaspoons finely chopped flat-leaf parsley; ½ teaspoon fresh lemon juice; kosher salt; 1 large beefsteak tomato; 4 brioche buns, split in half and toasted; mayonnaise; 2 avocados, halved and cut into 12 slices; ground black pepper; olive oil; ¼ cup pickled onions; 1 cup alfalfa sprouts