Begin by mixing the chili powder, garlic powder, paprika, onion powder, black pepper, and salt in a bowl. Generously rub this spice mix over both sides of the steak. Heat a cast iron skillet over medium-high heat. When hot, add the steak and cook for about 3 minutes per side for medium-rare. Adjust cooking time based on steak thickness and desired doneness. Once done, transfer to a plate and allow to rest for 5 minutes before slicing thinly against the grain.

Reduce the heat to medium and add a tablespoon of oil to the same skillet. Toss in the sliced bell peppers and onions. Stir occasionally and cook for 5-6 minutes, until the onions caramelize slightly, and the peppers become tender. Remove the veggies from the skillet and set aside.

Heat your skillet to medium-high. Place a large tortilla in the center and sprinkle a thin layer of shredded cheese evenly across one half. Arrange the steak strips and fajita veggies over the cheese, then top with another layer of cheese. Fold the tortilla in half to create a half-moon shape.

Allow the bottom of the quesadilla to cook for about 2 minutes or until golden brown and crispy. Carefully flip it with a spatula and cook the other side for another 1-2 minutes. The cheese should melt completely, and the tortilla should have a crispy, golden finish.

Remove the quesadilla from the skillet, slice it into triangular pieces, and serve warm with your favorite toppings or dips.