Preheat your oven to 375 degrees Fahrenheit (190°C) to so it's ready when your fajitas are prepared. Cover a large rimmed sheet pan with parchment paper.
Prepare the Chicken and Veggies: In a large mixing bowl, add the diced chicken, olive oil, paprika, garlic powder, onion powder, chili powder, dried oregano, cumin, salt, and black pepper to the bowl. Mix until well combined. Then add the minced garlic, sliced red, yellow, and orange bell peppers, and sliced red onion. Mix everything together until the chicken and veggies are evenly coated with the spices and oil.
Arrange on a Sheet Pan: Spread the seasoned chicken and veggies evenly across the sheet pan. Make sure they're in a single layer. This will help them cook evenly.
Bake the Fajitas: Place the sheet pan in the preheated oven and bake for 20-23 minutes or until the chicken is fully cooked to an internal temperature of 165 degree F. Make sure to check the chicken for doneness with an instant read thermometer, as cooking times may vary slightly depending on your oven.
Assemble Your Fajitas: Once your chicken fajitas are cooked to perfection, it's time to assemble your meal. Warm your tortillas according to package instructions or personal preference.
Toppings and Serving: Place a generous portion of the cooked chicken and veggie mixture onto each tortilla. Squeeze fresh lime juice over the filling, add diced avocado, a dollop of Greek yogurt, a sprinkle of shredded mozzarella, and a garnish of chopped cilantro.