Beef Torta Sandwich

Name: Beef Torta Sandwich
Prep time: 20 min
Cook time: 25 min
Total time: 45 min
Yield: 4
Ingredients: Ingredients; 4 crusty Mexican bolillo rolls or French bread rolls, halved; 5 lbs flank steak or sirloin, thinly sliced; 2 tablespoons vegetable oil; 1 teaspoon chili powder; 1/2 teaspoon cumin; Salt and black pepper to taste; 1 can (15 oz) black beans, drained and rinsed; 2 cloves garlic, minced; 1 ripe avocado, sliced; 1 cup fresh cilantro leaves; 1/2 red onion, thinly sliced; 4 oz queso fresco or Monterey Jack cheese, sliced; Quick Pickled Onions; 1/4 cup white vinegar; 1 tablespoon sugar; 1/2 teaspoon salt; 1/4 red onion, thinly sliced