Step 1

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.

Step 2

Do Ahead: Pickles can be made 2 weeks ahead. Keep chilled.

Step 3

Whisk buttermilk, yogurt, lemon juice, and 3 Tbsp. oil in a large bowl until smooth; season dressing with salt and pepper.

Step 4

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.

Step 5

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.