To make the chipotle sauce, combine all the ingredients in a blender or food processor and blend until smooth. Set aside.
Combine all the seasonings for the steak in a small bowl. Mix well.
Coat the steak with vegetable oil and season it thoroughly with the spice mixture, ensuring even coverage.
Heat a cast-iron skillet over medium-high heat. Cook the steak to your desired doneness. Remove it from the heat and let it rest briefly before cutting it into small, bite-sized strips. Wipe out the skillet with a paper towel.
In a medium bowl, toss together the Colby-Jack and mozzarella cheese.
Place the cleaned skillet over medium-high heat. Place one tortilla in the skillet. On one half of the tortilla, layer 1/2 cup of shredded cheese and a quarter of the seasoned steak pieces. Drizzle with chipotle sauce. Fold the other half of the tortilla over the fillings to create a half-moon shape. Cook until the cheese melts and the tortilla becomes golden brown. Flip and cook the other side until crispy. Repeat with the remaining tortillas.
Recipe Tips
The secret to achieving the perfect Taco Bell-style quesadilla is cooking it in a completely dry skillet. Any added oil or butter changes the texture of the tortilla. For authentic results, be generous with the cheese and sauce, but don't overload with steak, as Taco Bell uses a moderate amount of meat. If your chipotle sauce is too spicy, add a bit more sour cream to mellow it. For the most authentic experience, allow the quesadilla to cool for 1-2 minutes before cutting, which helps the cheese set slightly as it would when served at the restaurant.