Cut the chicken breasts into long stripes. Season with cumin, smoked paprika, garlic powder, cayenne pepper, salt and pepper.
Cut the bell peppers into long slices and then cut them in half. Cut the onion in half and then slice it thinly.
Heat the vegetable oil in a large skillet. Add chicken and cook it until it is golden and cooked through (5-7 minutes). Then add bell peppers and onion. Cook for a few more minutes. Adjust seasoning before serving.
Serve with warm tortillas, guacamole, hot sauce, fresh cilantro and your other favorite toppings.