Make the pickled vegetables: Combine cucumber, carrot, jalapeño, vinegar, water and one tablespoon sugar and salt to taste in a medium bowl; mix lightly. Refrigerate until ready to serve.
Prepare the sausage burgers: Combine sausage, 1 tablespoon of hot chili sauce, fish sauce, garlic, green onion, corn starch and 1 teaspoon of remaining sugar; mix lightly. Season to taste with salt and pepper; if desired. Shape mixture into four ½-inch-thick patty.
Cook in a large skillet over medium heat 12-15 minutes or until done (160 degrees F), turning frequently for even browning.
Combine mayonnaise with remaining 1 tablespoon hot chili sauce.
Fill each brioche bun with a burger patty, spicy mayonnaise, pickled vegetables and cilantro leaves, if desired.