Add the avocado oil, fresh lime juice, chili powder, ground cumin, garlic powder, paprika, oregano, salt, and pepper to a medium size low shallow bowl and mix well. Add in the chicken slices and toss to combine. Cover the bowl with plastic wrap and marinate the chicken for 2 hours. Remove the chicken from the marinade and discard it.
Preheat your Blackstone griddle grill to medium-high heat. Brush it with high-heat oil (such as avocado oil).
Add chicken to one side of the preheated griddle and the peppers and onions to the other. Cook for about 6-8 minutes until the chicken and vegetables are a little charred and the internal temperature of the chicken is 165 F when tested with a digital meat thermometer.
Combine the chicken, onions, and bell peppers together. Remove the Blackstone fajitas from the griddle and set them aside.
Heat the tortillas on the griddle for about 1 minute to warm them up.
Immediately serve the chicken fajitas with warm tortillas and toppings such as salsa, fresh cilantro, guacamole, and sour cream. Enjoy!