In a small bowl, combine chili powder, ground cumin, smoked paprika, cayenne pepper, dried oregano, salt, and black pepper. Mix well to create the fajita seasoning.
Place the thinly sliced chicken breast in a large bowl. Add half of the fajita seasoning and 1/2 tablespoon of olive oil. Toss to coat the chicken evenly and set aside.
Heat 1/2 tablespoon of olive oil in a large skillet over medium-high heat.
Add the sliced onions and bell peppers to the skillet. Cook, stirring occasionally, for about 5-6 minutes until the vegetables are tender-crisp. Remove the vegetables from the skillet and set aside.
Add the seasoned chicken to the same skillet. Cook for 6-7 minutes, stirring occasionally, until the chicken is cooked through and lightly browned.
Add the minced garlic and the remaining fajita seasoning to the skillet with the chicken. Stir and cook for an additional 1 minute until fragrant.
Return the cooked bell peppers and onions to the skillet. Stir everything together and cook for another 1-2 minutes to combine flavors. Remove from heat.
Warm the whole wheat tortillas in a dry skillet or microwave for 20 seconds.
To assemble, divide the chicken and vegetable mixture evenly among the tortillas.
Garnish with chopped fresh cilantro and serve with lime wedges on the side for squeezing over the fajitas.