Preheat oven to 400°F. Spray a large baking sheet with cooking spray and set aside.
In a small bowl add all the seasonings, chili powder, paprika, cumin, oregano, and salt. Stir to combine.
Place the chicken breasts in a large mixing bowl or large sealable plastic bag. Pour half of the olive oil over the chicken and sprinkle about 1/3 of the fajita seasoning mix.
Stir to coat the chicken in the seasoning, or seal the bag and shake to coat. Place the chicken on the baking sheet.
Add the sliced peppers and onion to the same bowl or bag and repeat with the remaining olive oil and fajita seasoning. Spread on the baking sheet in an even layer.
Bake for about 30-35 minutes or until chicken is fully cooked.
Allow the chicken to rest for about 5 minutes then slice into strips. Squeeze lime juice over the chicken and peppers. Garnish with cilantro if desired.
Heat tortillas, either on burners on stove or in microwave. Heating over the burner will give your tortillas a charred appearance and flavor.