Boil tortellini in salted water per instructions on package. White boiling, heat oil in pan (I used flat bottom wok), stir in tomato and onion and simmer a bit. Squeeze lemon into skillet (use fork ). One to two glugs of white wine (pino grigio). Salt and pepper to taste. As tortellini is cooking, scoop pasta water into sauce as needed. Add butter to enrich. Stir in parsley. Scoop cooked tortellini from pot into skillet with sauce and toss. Serve with grated parmesan.