01 - Preheat a grill pan or large skillet over medium-high heat. Rub the steak with olive oil, then coat evenly with chili powder, cumin, salt, and pepper. Sear for 3 to 4 minutes per side for medium-rare, adjusting time for preferred doneness.
02 - Transfer the steak to a cutting board and let rest for 5 minutes to allow juices to redistribute. Slice thinly against the grain.
03 - In the same pan, add the sliced bell pepper, onion, and jalapeño. Sauté over medium-high heat until softened and lightly golden, about 5 minutes. Remove from heat and set aside.
04 - Lay each tortilla flat. On one half, layer sliced steak, sautéed vegetables, and shredded cheese. Fold the tortilla over to enclose the filling, pressing gently to seal.
05 - Wipe the pan clean and return to medium heat. Cook each quesadilla for 2 to 3 minutes per side, pressing down lightly with a spatula, until the tortilla is golden brown and the cheese is fully melted.
06 - Transfer quesadillas to a cutting board and slice each into wedges. Serve immediately with sour cream, salsa, chopped cilantro, and lime wedges on the side.