Preheat the oven to 400. Place chicken strips in a greased 9 x 13 baking dish. In a small bowl combine the oil, chili powder, cumin, garlic powder, dried oregano and salt. Drizzle the spice mixture over the chicken and stir to coat. Next add the tomatoes, peppers and onions to the dish and stir to combine. Bake uncovered for 20-25 minutes or until chicken is cooked through and veggies are tender. Serve in fajitas shells with lettuce, cheese and salsa.