Heat oil in a large frypan over medium high heat. Saute mushrooms, capsicum and onion until soft; remove from frypan and set aside. Saute chicken for about 15 minutes or until cooked through and juices run clear. Return mushroom mixture to frypan and stir all together.
Bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain.
Return pasta to pot over medium heat and stir in spaghetti sauce; heat through then stir in chicken mixture and heat through, stirring. Serve hot.