Hot and Sour Seafood Soup

Name: Hot-and-Sour Seafood Soup
Ingredients: 1/2teaspoon sugar; 1/4cup cornstarch; 12ounces firm white fish (such as pollock), cut into 1 inch pieces; 1bunch scallions; whites cut into 1/4 inch pieces,greens cut into 2 inch pieces; 1tablespoon low sodium soy sauce; 1tablespoon minced peeled ginger; 1tablespoon vegetable oil; 2plum tomatoes, cored and cut into large chunks; 2tablespoons balsamic vinegar; 4ounces shiitake mushrooms, stemmed and sliced; 6ounces bay scallops; Kosher salt and freshly ground pepper