Heat the olive oil in a large skillet over medium-high heat.
Add the chicken slices and cook until lightly browned and nearly cooked through, about 5 minutes.
Add the bell pepper and onion to the skillet, stirring frequently, until vegetables are tender and chicken is fully cooked, about 5 more minutes.
Stir in chili powder, cumin, garlic powder, and season with salt and pepper.
Warm the tortillas according to package instructions.
Divide the chicken and vegetable mixture among the tortillas. Add optional garnishes such as lime, cilantro, and avocado if desired.
Serve immediately.
