Beef Taco Salad with Homemade Tortilla Bowls

Name: Beef Taco Salad with Homemade Tortilla Bowls
Ingredients: 4 10-inch flour tortillas; vegetable oil spray; 1 tablespoon vegetable oil; 1 onion, finely chopped; 2 tablespoons chili powder; 3 garlic cloves, minced; 1 pound lean ground beef; 1 (8-ounce) can tomato sauce; 1/2 cup chicken broth; 2 teaspoons cider vinegar; 1 teaspoon packed light brown sugar; salt and pepper; 2 romaine lettuce hearts, shredded; 1 (15-ounce) can black beans, drained and rinsed; 8 ounces cherry tomatoes, quartered; 2 scallions, thinly sliced; 1/4 cup chopped fresh cilantro; 2 tablespoons lime juice; 1/2 cup shredded Mexican cheese blend; avocado, for topping (optional); sour cream or Mexican crema, for topping (optional)