01 - In a mixing bowl, toss the thinly sliced steak with olive oil, ground cumin, smoked paprika, garlic powder, salt, black pepper, and lime juice. Let the meat marinate for 10 minutes to absorb the seasonings.
02 - Heat a large skillet or grill pan over medium-high heat. Sear the marinated steak slices for 2 minutes per side until nicely browned but still tender. Remove from the pan and set aside.
03 - In the same pan, sauté the sliced red onion and bell pepper along with the jalapeño if using. Cook for 3 to 4 minutes until the vegetables are softened and slightly charred.
04 - Wipe the skillet clean and return it to medium heat. Lay a flour tortilla flat in the pan and sprinkle one quarter of the shredded cheese over one half. Layer the seared steak, sautéed vegetables, and fresh cilantro on top of the cheese, then fold the tortilla over to enclose the filling.
05 - Cook the quesadilla for 2 to 3 minutes per side, pressing down lightly with a spatula, until the tortilla is golden brown and the cheese has fully melted.
06 - Repeat the assembly and cooking process with the remaining tortillas and filling. Allow each quesadilla to rest briefly before slicing into wedges. Serve hot alongside salsa, sour cream, and guacamole.