01 - In a mixing bowl, toss the sliced steak with olive oil, ground cumin, smoked paprika, garlic powder, salt, black pepper, and lime juice until evenly coated. Let rest for 10 minutes to absorb the flavors.
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. Transfer to a plate and set aside.
03 - In the same pan, sauté the sliced onion and bell pepper along with the jalapeño if using. Cook for 3 to 4 minutes until the vegetables are softened and lightly charred. Remove from the pan and set aside.
04 - Wipe the skillet clean and return it to medium heat. Lay a flour tortilla flat in the pan. Sprinkle one quarter of the shredded cheese over one half of the tortilla, then layer the seared steak, sautéed vegetables, and fresh cilantro on top of the cheese. Fold the empty half of the tortilla over the filling to close.
05 - Cook the quesadilla for 2 to 3 minutes per side, pressing down lightly with a spatula, until the tortilla is golden brown and crispy and the cheese is fully melted.
06 - Repeat the assembly and cooking process with the remaining tortillas, steak, vegetables, cheese, and cilantro.
07 - Allow the quesadillas to rest for 1 to 2 minutes before slicing into wedges. Serve hot alongside salsa, sour cream, and guacamole.