Prep the peppers: Preheat your oven to 400°F (200°C). Halve the bell peppers lengthwise and remove the seeds and membranes.
Place them cut-side up in a baking dish. Drizzle with a little olive oil and sprinkle with a pinch of salt.
Par-bake: Bake the peppers for 10 minutes to soften slightly. This helps them cook through without getting watery later.
Set aside.
Sauté the aromatics: Heat 1 tablespoon olive oil in a large skillet over medium heat. Add the sliced onion and cook until soft and lightly browned, about 5–7 minutes. Stir in the garlic and cook 30 seconds until fragrant.
Season the filling: Add the cooked chicken to the skillet.
Sprinkle in chili powder, cumin, smoked paprika, oregano, cayenne (if using), salt, and black pepper. Stir well to coat and warm through.
Stir in veggies: Add diced tomatoes, corn, and black beans (if using). Cook 2–3 minutes to combine and reduce excess moisture.
Squeeze in lime juice and adjust salt to taste. Remove from heat and stir in chopped cilantro.
Fill the peppers: Spoon the chicken fajita mixture into each pepper half, packing it gently. Top each with shredded cheese.
Bake: Return the dish to the oven and bake 12–15 minutes, until the peppers are tender and the cheese is melted and bubbly.
For a golden top, broil for 1–2 minutes at the end, watching closely.
Finish and serve: Let the peppers rest for 5 minutes. Garnish with extra cilantro and serve with lime wedges, sour cream, avocado, or salsa as you like.