Preheat the oven to 400°F (200°C). Line or lightly oil a large sheet pan.
Slice the chicken breasts into thin strips, about ½-inch wide, cutting against the grain.
Add the sliced chicken, bell peppers, and onion to the pan.
Drizzle with olive oil and sprinkle with fajita seasoning, tossing until evenly coated.
Spread the mixture into a single layer and bake for 20-25 minutes, stirring halfway, until the chicken reaches 165°F and the veggies are tender.
Sprinkle the warm fajita filling with shredded cheese so it melts slightly, then finish with a squeeze of lime.
Serve hot with warm tortillas and toppings.