- 2 cups apple cider vinegar
- 1/2 cup (packed) light brown sugar
- 1/4 cup kosher salt
- 4 cups any combination shredded carrots, sliced cucumbers, sliced red onions, and/or sliced mild fresh chiles
- 1/4 cup buttermilk
- 1/4 cup plain whole-milk Greek yogurt
- 1 tablespoon fresh lemon juice
- 6 tablespoons olive oil, divided
- Kosher salt, freshly ground pepper
- 2 ripe avocados, halved
- 6 ounces fresh goat cheese
- 6 cups mixed lettuce leaves, ribs removed if thick
- 8 slices multigrain bread, toasted
- 1/2 English hothouse cucumber, thinly sliced on a diagonal
- 2 cups sprouts
- 2 heatproof 1-qt. glass jars
- Bring vinegar, brown sugar, salt, and 2 cups water to a boil in a large saucepan. Meanwhile, pack vegetables into jars. Pour brine over vegetables. Cover and chill until cool.
- Whisk buttermilk, yogurt, lemon juice, and 3 Tbsp. oil in a large bowl until smooth; season dressing with salt and pepper.
- Scoop avocados into a small bowl; add 1 Tbsp. oil and lightly mash. Season with salt and pepper. Mash goat cheese with remaining 2 Tbsp. oil in another small bowl until softened and spreadable; season with salt and pepper.
- Add lettuce to dressing and toss to coat; season with salt and pepper. Spread avocado mixture over 4 slices of bread. Arrange lettuce over and top with cucumber, sprouts, and some drained pickles. Spread remaining 4 slices of bread with goat cheese and close sandwiches.
- Pickles can be made 2 weeks ahead. Keep chilled.