These carne asada quesadillas are the kind of meal you make when you want something hot, cheesy, with tender flank steak, melty Monterey Jack, green chiles, and fresh cilantro all tucked inside a crispy, buttery tortilla.
Set aside 1/2 teaspoon of the rub for later. Season the flank steak with the remaining carne asada rub and 1 tablespoon of the olive oil. Rub it in with your hands to really coat the meat. Let sit in the refrigerator covered for at least 30 minutes.
Heat a pan over medium-high heat. Add the remaining olive oil. When hot, sear the steak for 3 minutes per side, or until your desired internal temperature. I do 135° F for medium-rare. Transfer to a plate to rest for 5 minutes.
Cut the carne asada into small pieces.
Heat a cast iron skillet over medium heat.
Brush one side of the tortilla with melted butter and place it buttered-side down on the pan. Top with equal amounts carne asada, cheese, green chilis, green onions and cilantro. Add the top tortilla. Brush the top with melted butter.
Cook for 4-5 minutes per side, until browned and heated through.
Top with sour cream, more green onion and cilantro and sprinkle with the reserved carne asada rub.