Barbecued Salmon Sandwiches

Name: Barbecued Salmon Sandwiches
Ingredients: 1 tablespoon vegetable oil; 1/4 cup finely chopped onion; 1 garlic clove, minced; 1/2 cup ketchup; 1 chipotle in adobo, finely chopped; 1 teaspoon Worcestershire sauce; 1/2 teaspoon dry mustard; 2 tablespoons cider vinegar; 3 tablespoons mayonnaise; Kosher salt and freshly ground pepper; 1 1/2 cups coleslaw mix; 1 1/2 tablespoons finely chopped cilantro; 1 scallion, thinly sliced; Four 5-ounce skin-on salmon fillets; 4 hot dog buns, preferably brioche-style or split-top