Bring a large pot of lightly salted water to a boil. Cook linguine at a boil until tender yet firm to the bite, about 11 minutes. Drain and transfer to a serving bowl.
Melt butter in a large skillet over medium heat. Add mushrooms; cook and stir until tender and lightly browned, about 5 minutes. Stir in parsley, salt, and black pepper; cook until flavors combine, about 1 minute. Pour in heavy cream. Bring to a gentle boil; cook until sauce thickens slightly, about 5 minutes.
Pour sauce over pasta in the serving bowl; toss to combine. Add green onions and Parmesan cheese; toss until combined.