Make the Salsa:
Heat olive oil in a pan over medium heat. Add the tomatillos and onion, searing for 4 to 5 minutes. Remove from heat.
Add the seared tomatillos and onions to a food processor along with garlic, cilantro, avocado, lime juice, jalapeños, and salt. Blend until smooth.
Transfer the salsa to a bowl and set aside.
Make the Carne Asada:
In a large bowl, combine olive oil, orange juice, lime juice, soy sauce, white vinegar, smoked paprika, cumin, oregano, salt, garlic powder, onion powder, cayenne, and black pepper. Whisk to create a marinade.
Add the flap steak to the marinade, mixing to coat evenly. Cover and let marinate for at least 30 minutes, or overnight for more flavor.
Preheat a skillet or grill over high heat. Add the steak and sear for 3 to 4 minutes on each side, or until browned and cooked to your desired level. Slice the steak into thin strips or cubes.
Assemble the Tortas:
Spread refried beans on the bottom of each toasted telera roll.
Top with carne asada, Oaxaca cheese, cotija cheese, lettuce, avocado slices, white onion, cilantro, and sour cream.
Drizzle with the tomatillo salsa, seal the sandwich shut, and serve.