Chicken Thigh Bulgogi Tacos

Name: Chicken Thigh Bulgogi Tacos
Ingredients: 0.25 cup white wine vinegar; 1 teaspoon white sugar, or more to taste; salt and ground black pepper to taste; 2 Persian cucumbers, halved and thinly sliced; 1 tablespoon olive oil; 1 (8 ounce) package shredded red cabbage; 4 scallions, sliced, whites and greens separated; 1.5 pounds skinless, boneless chicken thighs, cut into 1-inch cubes; 1 cup Korean bulgogi sauce; 1/3 cup sour cream; 1 tablespoon water; 0.5 tablespoon sriracha sauce, or to taste; 8 (6 inch) flour tortillas, or more as needed