Pat the sirloin steak dry with a paper towel. In a small bowl, mix together the chili powder, cumin, garlic powder, salt, and pepper. Rub the seasoning mixture generously over all sides of the steak.

Heat olive oil in a large skillet over medium-high heat. Place the seasoned steak in the hot skillet and cook for 3-4 minutes per side for a perfect medium-rare. Adjust timing for your desired level of doneness. Remove the steak from the pan and let it rest on a cutting board for at least 10 minutes.

While the steak is resting, add the sliced bell pepper and onion to the same skillet. Sauté for 5-7 minutes, stirring occasionally, until the vegetables are softened and lightly caramelized. Remove them from the skillet.

Once rested, thinly slice the steak against the grain.

Wipe the skillet clean and return it to medium heat. Place one flour tortilla in the skillet. Sprinkle about 1/2 cup of the shredded cheese blend over the tortilla. Arrange a quarter of the sliced steak and sautéed vegetables over one half of the tortilla.

When the cheese is melted, fold the tortilla in half over the filling. Press down gently with a spatula and cook for 2-3 minutes, until the bottom is golden brown and crispy. Flip and cook the other side for another 2 minutes.

Remove the quesadilla from the skillet, let it cool for a moment, then slice into wedges. Repeat the process for the remaining tortillas and filling. Serve immediately with your favorite toppings.