Cook the pasta according to package instructions.
While the pasta ist cooking, heat olive oil over medium high heat, add chopped chicken. Brown it on all sides until just cooked, but don’t worry if it’s not super well cooked all the way through. It will be heated up again in the end.
Remove chicken into bowl and set aside.
Add the stick of butter, the mushrooms and the onions. Cook until soft.
Add the garlic and the cheese, let melt into sauce.
Add the peas and pre-cooked chicken. Stir.
Toss it all together with the cooked and draines pasta, adding a splash of reserved pasta sauce, if needed to make the sauce really come together. Toss well and sprinkle with chopped parsley.