Two 12-ounce jars red-pepper relish, such as Fourth Creek Food Co.
1 small onion, chopped
2 cloves garlic, chopped
1 tablespoon plus 1 teaspoon extra-virgin olive oil, plus more for brushing
2 tablespoons low-sodium soy sauce
2 pounds ground dark turkey
4 teaspoons Worcestershire sauce
1 teaspoon Dijon mustard
1 slice soft white bread, torn into pea-size pieces (1 cup)
Kosher salt and freshly ground black pepper
3 tablespoons chili sauce, plus more for brushing
1/2 cup mayonnaise
2 packed cups finely shredded kale
1/2 teaspoon balsamic vinegar
8 brioche rolls, split
4 tablespoons unsalted butter, melted