In a large bowl, combine chili powder, ground cumin, smoked paprika, dried oregano, salt, black pepper, cayenne pepper, and minced garlic.
Add 2 tablespoons olive oil and fresh lime juice to the spice mixture and stir to create the marinade.
Add the thinly sliced chicken breasts to the marinade and toss to coat evenly. Cover and refrigerate for at least 1 hour or up to overnight.
Preheat a large skillet or cast-iron pan over medium-high heat and add 1 tablespoon olive oil.
Add the sliced onions and bell peppers to the skillet and sauté for 5-7 minutes until they are tender-crisp. Remove from skillet and set aside.
In the same skillet, add the marinated chicken slices in a single layer. Cook for 6-8 minutes, stirring occasionally, until the chicken is cooked through and slightly browned.
Return the cooked peppers and onions to the skillet with the chicken and stir to combine. Cook together for 2 more minutes to blend flavors.
Allow the chicken fajita mixture to cool completely before transferring to airtight containers. Refrigerate for up to 3 days or freeze for up to 1 month.
To serve, reheat the chicken and vegetable mixture in a skillet over medium heat until warmed through.
Warm the flour tortillas in a dry skillet or microwave.
Serve the chicken fajita mixture on warm tortillas with optional shredded cheddar cheese, sour cream, chopped cilantro, and salsa.