Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper for easy cleanup.
Slice the chicken breast, bell pepper, and red onion into thin, uniform strips to ensure even cooking.
Place the chicken and vegetables on the sheet pan, drizzle with olive oil, and sprinkle with chili powder, cumin, smoked paprika, sea salt, and black pepper.
Toss everything together until well-coated, then spread into a single layer across the pan.
Roast for 18 to 20 minutes, or until the chicken is cooked through and the vegetables are tender with slightly charred edges.
While the chicken roasts, warm the corn tortilla in a dry skillet over medium heat for 30 seconds per side.
Slice the avocado and squeeze fresh lime juice over the roasted chicken and vegetables before serving inside the warm tortilla.