Step 1: Preheat and Prepare the Pan
Preheat your oven to 400°F (200°C). Grab a large, rimmed baking sheet. Using a large pan is crucial; if the ingredients are too crowded, they will steam instead of roast, preventing them from developing those delicious caramelized edges. If needed, use two smaller baking sheets.

Step 2: Make the Fajita Seasoning
In a small bowl, combine all the fajita seasoning ingredients: chili powder, smoked paprika, cumin, garlic powder, onion powder, dried oregano, salt, black pepper, and cayenne pepper. Whisk them together until they are thoroughly mixed. This ensures an even distribution of flavor.

Step 3: Season the Chicken and Vegetables
Place the sliced chicken, sliced bell peppers, and sliced onion directly onto the prepared baking sheet. Drizzle them with the 3 tablespoons of olive oil. Sprinkle about three-quarters of the homemade fajita seasoning blend over the ingredients. Using your hands or a pair of tongs, toss everything together until the chicken and vegetables are evenly coated in oil and spices.

Step 4: Arrange for Roasting
Spread the chicken and vegetable mixture into a single, even layer on the baking sheet. This is the most important step for achieving a proper roast. A single layer allows hot air to circulate around each piece, promoting browning and caramelization.

Step 5: Bake to Perfection
Place the baking sheet in the preheated oven and bake for 20-25 minutes. The cooking time will vary depending on the thickness of your chicken strips. The chicken should be cooked through (reaching an internal temperature of 165°F or 74°C), and the vegetables should be tender-crisp and slightly charred at the edges.

Step 6: Add the Cheese and Broil (Optional but Recommended)
Carefully remove the baking sheet from the oven. Sprinkle the remaining fajita seasoning over the top for an extra flavor boost. Evenly distribute the 2 cups of shredded cheese over the chicken and vegetables.

Step 7: The Final Melt
Return the baking sheet to the oven. You can either bake for another 3-5 minutes, just until the cheese is melted and bubbly, or for a restaurant-style finish, switch your oven to the broil setting. Broil for 1-2 minutes, watching it very closely, until the cheese is bubbling and has beautiful golden-brown spots. The broiler is intense, so do not walk away during this step!

Step 8: Rest and Garnish
Remove the pan from the oven and let it rest for a few minutes. This allows the juices in the chicken to redistribute, ensuring a tender bite. Garnish generously with fresh chopped cilantro and serve immediately with lime wedges on the side for squeezing.