Cook fettuccine in a large saucepan of salted boiling water following the packet directions until al dente. Drain. Set aside.
Meanwhile, heat oil in a large frying pan or wok over medium-high heat. Add onions. Saute for 2-3 minutes or until soft and translucent. Add garlic. Saute for 1-2 minutes or until aromatic.
Add chicken. Cook, stirring occasionally, for 5-6 minutes or until chicken is cooked through. Add mushrooms. Cook, stirring occasionally, for 2-3 minutes or until tender.
Add cream and crushed stock cubes. Season with salt and pepper. Cook again, stirring occasionally, for another 4-5 minutes.
Return pasta to the pan. Add cheese and basil. Toss until well combined. Add green peas. Toss until well combined. Cook until heated through.
Garnish with more chopped basil and cheese if you like.