Place chicken and flour in a large resealable plastic bag; seal bag and shake to coat. Heat 1 tablespoon oil in a large frypan over medium heat. Shake excess flour off chicken and saute in oil for 4 to 5 minutes each side, or until golden brown and cooked through (juices run clear). Remove from frypan and place in a medium bowl; set aside.
Bring a large pot of lightly salted water to a boil. Add spaghetti and cook for 8 to 10 minutes or until al dente; drain, reserving 2/3 cup cooking water, and return pasta to pot. Set aside pasta and cooking water.
Wipe frypan with paper towel. Heat 1 teaspoon oil in frypan over medium heat. Add green capsicum, red capsicum, yellow capsicum, onion and garlic and saute for 3 minutes. Cover, reduce heat to low and cook 3 minutes more or until vegetables are tender.
Stir in Alfredo sauce, cover and heat for 1 to 2 minutes. Remove from heat and add to reserved pasta in pot, then add reserved cooking water and chicken. Toss to mix, pour into serving bowls and sprinkle with fresh chopped parsley.