Bring a large pot of salted water to a boil.
Boil tortellini until tender, 3–4 minutes. Reserve 1/2 cup pasta water; drain.
Pat shrimp dry. Season with a pinch of salt and pepper.
Heat olive oil in a large skillet over medium-high. Sear shrimp until opaque, 2–3 minutes. Transfer.
Reduce heat to medium. Melt butter in the skillet.
Sauté garlic 30 seconds until fragrant; do not brown.
Pour in cream. Simmer until slightly thickened, 3–4 minutes. Whisk in Parmesan until smooth.
Stir in lemon juice and red pepper flakes.
Add tortellini and shrimp to the sauce. Toss gently to coat.
Splash in pasta water as needed to loosen the sauce.
Finish with parsley. Taste and adjust salt and pepper. Serve hot.