Preheat your oven to 400°F and line a large sheet pan with parchment paper for easy cleanup.
Slice the chicken breast, bell peppers, and red onion into thin, even strips.
Place the chicken and vegetables on the sheet pan, drizzle with olive oil, and sprinkle with chili powder, cumin, garlic powder, salt, and 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.
While the mixture roasts, mash the avocado in a small bowl with lime juice and a pinch of salt until creamy.
Warm the tortilla in a dry skillet or directly over a low gas flame for a few seconds per side until pliable.
Fill the warm tortilla with the roasted chicken and pepper mixture, top with a dollop of guacamole, and garnish with fresh cilantro.