Step 1: Prepare Your Ingredients. Slice the chicken breasts against the grain into thin, uniform strips (about 1/4 to 1/2 inch thick). Slice bell peppers (red, yellow, orange) and onion into similar-sized strips. Mince your garlic.
Step 2: Make the Fajita Seasoning. In a small bowl, combine chili powder, cumin, smoked paprika, garlic powder, onion powder, dried oregano, salt, and black pepper. Add a pinch of cayenne pepper if you like a little heat. Stir well to combine.
Step 3: Marinate the Chicken. In a medium bowl, toss the sliced chicken with 1 tablespoon of olive oil, the fresh lime juice, and half of the prepared fajita seasoning. Mix until the chicken is evenly coated. Let it marinate for at least 15 minutes at room temperature, or cover and refrigerate for up to 30 minutes for deeper flavor.
Step 4: Sauté the Vegetables. Heat 1 tablespoon of olive oil in a large skillet (cast iron works wonderfully here!) over medium-high heat. Add the sliced bell peppers and onion. Sauté for 5-7 minutes, stirring occasionally, until the vegetables are tender-crisp and slightly charred. Remove the vegetables from the skillet and set aside.
Step 5: Cook the Chicken. Add the remaining 1 tablespoon of olive oil to the same skillet (no need to clean it). Increase the heat to high. Once the oil is shimmering, add the marinated chicken in a single layer, making sure not to overcrowd the pan. You may need to cook the chicken in batches to achieve a good sear. Cook for 3-4 minutes per side, or until the chicken is cooked through and nicely browned. Avoid overcooking to keep the chicken juicy.
Step 6: Combine and Finish. Return the cooked vegetables to the skillet with the chicken. Sprinkle the remaining fajita seasoning over the chicken and vegetables. Toss everything together for 1-2 minutes until well combined and heated through.
Step 7: Serve Immediately. Serve your sizzling chicken fajitas immediately with warm tortillas and your favorite toppings.