Mix 2 tablespoon of olive oil, smoked paprika, chili powder, ground cumin, ½ teaspoon salt, black pepper, and adobo sauce into a bowl. Then, add sirloin steak and toss to coat. Cover it with plastic wrap and refrigerate for 30 minutes to 2 hours.
Add 1 tablespoon of olive oil into a skillet and place it over medium heat. Incorporate sliced green bell pepper and sliced onion, then add ½ teaspoon of salt. Sauté for 8 minutes, stirring regularly until soft. Once the onion is translucent, add minced garlic and stir for a minute. Remove from heat.
Cook the marinated steak in an iron-cast skillet over medium heat. Sear the meat from both sides for 2-3 minutes and cook until the desired meat doneness. I like to cook my meat medium or medium well, which is an internal temperature of around 140 degrees F. Before making the quesadillas, chop the meat into bite-sized pieces, slicing the steak against the grain. This ensures that the meat is tender and easy to bite into. Also, allow the steak to rest for a few minutes before slicing. This helps retain juices and ensures a juicy and tender filling for your quesadillas.
Prepare your quesadillas by adding shredded mozzarella, sauteed veggies, and steak to the flour tortillas. Then, add some butter into a preheated skillet, place the filled tortilla in the pan, and fold it in half. Cook until the cheese is melted and the tortilla is golden brown, usually 2-3 minutes per side.
For added freshness and flavor, serve the steak quesadillas with your favorite toppings, such as salsa, guacamole, sour cream, or chopped cilantro.