Cook fettuccine according to package directions; drain. Meanwhile, in a large nonstick skillet, heat 1 Tbsp. of the oil over high heat. Add chicken; cook and stir until golden on all sides, about 5 minutes; remove to a plate. Heat remaining 1 Tbsp. oil in the skillet. Add mushrooms; sauté until lightly browned and liquid has evaporated, about 5 minutes. Reduce heat to medium-low. Return chicken to skillet; stir in Alfredo sauce and 1 cup peas, if desired. Cover and simmer until sauce is hot, about 3 minutes, stirring occasionally. Serve over fettuccine, sprinkled with parsley, if desired. Makes 4 servings.