Weeknight Pulled Pork With Chipotle Barbecue Sauce

Name: Weeknight Pulled Pork With Chipotle Barbecue Sauce
Ingredients: 2 tbsp sugar; ⅛ tsp salt; ¼ cup vinegar; ½ red onion, very thinly sliced; 3 tbsp oil; 1 large onion, chopped (finely if not if not using immersion blender, otherwise coarse is fine); 4 cloves garlic, minced; 1-2 tbsp chipotle in adobo sauce (minced, if not using immersion blender); 1 cup ketchup; ⅓ cup white vinegar; ¼ cup brown sugar; ¼ cup soy sauce; ½ cup water; 2 pork tenderloins (about 1¾ lbs total), cut in thirds; Buns or warmed corn/flour tortillas for serving; Sour cream, cilantro, sliced avocado for topping (optional)