Melt 1/4 cup butter in a large skillet; add chicken and sauté until lightly browned. Remove chicken from skillet and set aside. Leave the pan drippings in skillet. Add mushrooms, green onions, 1/2 teaspoon salt, 1/4 teaspoon pepper and 1/4 teaspoon garlic powder to skillet. Sauté until vegetables are tender. Add chicken; simmer 20 minutes or until chicken is done. Cook fettuccine according to package directions, omitting salt. Drain noodles. Combine 1/2 cup melted butter and remaining ingredients except cheese and pecans. Stir into fettuccine. Add cheese, tossing until mixed well. Add chicken and vegetable mixture and toss. To serve, arrange on platter and sprinkle with pecans. Serves 6.