Combine all of the marinade ingredients except for the meat and orange slices in a large bowl and whisk to combine. Place meat a large ziplock bag. Pour the marinade over the steak, add orange slices and seal the bag. Refrigerate for at least 6 hours or overnight.
Heat an outdoor grill to medium-high heat. Remove the steak from the marinade and place onto the grill. Cook the steak until it has reached medium rare (or more if you prefer). Remove the meat from the grill and cut into thin strips.
Combine all of the ingredients for the lime-avocado sauce in a food processor and blend until smooth. Add more oil if the sauce is too thick. Set aside.
Heat a large skillet to medium heat. Butter one side of a tortilla. Lay the tortilla into the skillet butter-side down and sprinkle some of the cheese over the top of the entire tortilla. Add a layer of the carne asada steak onto one side of the tortilla.
Once the cheese has melted and the tortilla has browned on the bottom, fold the half with just the cheese over the half of the tortilla with the steak and press gently with a spatula. Cut into 3 slices and serve with the avocado-lime sauce on the side. Repeat with the remaining tortillas.