Cook tortellini according to package directions. Meanwhile, in a large skillet, saute onion in butter until tender.
Add the peas, mushrooms and ham; cook until mushrooms are tender. Stir in cream and pepper; heat through. Stir in the grated Parmesan cheese until melted.
Drain tortellini and place in a serving dish; add the sauce and toss to coat.
Sprinkle with shredded Parmesan cheese if desired.