Flank Steak with Orange and Avocado Salsa

Name: Flank Steak with Orange and Avocado Salsa
Ingredients: For the salsa; 2 tablespoons finely diced red onion; 2 tablespoons lime juice; 1 tablespoon white vinegar; 1 tablespoons olive oil; 1/4 teaspoon salt, or to taste; 1/8 teaspoon freshly ground black pepper; 4 to 5 oranges, any kind; 1/4 cup chopped cilantro leaves; For the steak; 1 1/2 pounds flank steak; 1 tablespoon plus 2 teaspoons olive oil; 2 teaspoons ancho chili powder; Salt and pepper, to taste; To serve:; 4 ounces queso fresco, crumbled; 1 avocado, sliced; 1/4 cup cilantro leaves; Warm tortillas or salad greens, for serving (optional)