In a large resealable plastic bag, combine 2 Tablespoons oil, lemon juice, seasoning packet and chicken. Seal and turn to coat. Refrigerate for 1-4 hours.
In a large sauté pan, on medium high heat, add 2 Tablespoons of oil. Heat for 1 minute and add onion and peppers. Cook for 2-3 minutes or until tender crisp. Place on plate and keep warm.
In same pan, add the marinated chicken and cook on medium high heat for 5-6 minutes or until meat is no longer pink. Return onion pepper mixture to pan; heat through.
Serve with warmed tortillas, cheese, salsa, guacamole and sour cream.