Preheat oven to 425 degrees F.

Make Seasoning Mix. In a small bowl, combine chili powder, cumin, garlic and onion powder, smoked paprika, and salt. 

Combine Fajitas Mixture. In a large bowl (or right on the baking sheet if you want to save a dish), combine bell peppers and onion. Add chicken and cilantro. Sprinkle with spice mixture, and drizzle with lime juice and oil. Toss with tongs or your hand to combine well.

Roast. Spread fajitas mixture out on a baking sheet in a single layer. Bake at 425 degrees F. for 25-30 minutes, or until chicken is cooked through and peppers and onions are starting to char. (If you want, you can put the pan under the broiler for 1-2 minutes at the end to get more charring.)

Serve & Store. Serve the fajitas in tortillas with guacamole and salsa, or spoon onto burrito bowls, taco salads, etc. Leftover fajitas can be stored in an airtight container in the fridge 3-4 days.