In a large bowl, combine the chicken, lime juice, olive oil, chili powder, paprika, cumin, garlic powder, onion powder, oregano, salt, and pepper. Toss to coat the chicken evenly. Marinate for at least 30 minutes, or up to overnight in the refrigerator.
Heat a large skillet over medium-high heat. Add a thin layer of vegetable oil and swirl to coat the bottom. Add the chicken and cook until browned on all sides, about 5-7 minutes per side. Remove the chicken from the skillet and set aside.
Add the bell peppers and onions to the skillet and cook until softened and slightly charred, about 5-7 minutes.
Warm the tortillas in a dry skillet or microwave until soft and pliable.
Assemble the fajitas by filling each tortilla with chicken, peppers, onions, and your desired toppings.