Step 1: In a medium bowl, whisk together 2 tablespoons olive oil, lime juice, chili powder, cumin, smoked paprika, garlic powder, onion powder, oregano, cayenne pepper (if using), salt, and black pepper to create the marinade.
Step 2: Add the thinly sliced chicken to the bowl, tossing to ensure all pieces are thoroughly coated. Cover and refrigerate for at least 30 minutes, or up to 2 hours.
Step 3: Heat a large cast iron skillet or heavy-bottomed pan over medium-high heat until very hot. Add 1 tablespoon of olive oil.
Step 4: Add the sliced onions and bell peppers to the hot skillet. Cook, stirring occasionally, for 5-7 minutes, until they are tender-crisp and slightly charred. Remove the vegetables from the skillet and set aside.
Step 5: Add the remaining 1 tablespoon of olive oil to the same skillet. Increase heat if necessary. Add the marinated chicken in a single layer, making sure not to overcrowd the pan. You may need to cook the chicken in batches.
Step 6: Cook the chicken for 3-5 minutes per side, or until fully cooked through and beautifully seared with a slight crust.
Step 7: Return the cooked vegetables to the skillet with the chicken. Toss everything together to combine, letting the flavors meld for another minute or two.
Step 8: Remove the skillet from the heat. Squeeze fresh lime juice over the chicken and vegetables.
Step 9: Warm your tortillas according to package directions (microwave, dry skillet, or oven).
Step 10: Serve the sizzling chicken and vegetables immediately with warm tortillas and your favorite toppings like sour cream, salsa, guacamole, cheese, and fresh cilantro.